Method and apparatus for chroma intra prediction in video coding

ABSTRACT

Devices and methods of directional intra prediction for chroma component of a picture are provided. The method includes obtaining an initial intra prediction mode of the chroma component, and deriving a chroma intra prediction mode (intraPredModeC) from a look up table (LUT) by using the initial intra prediction mode of the chroma component. The chroma component has different subsampling ratios in horizontal and vertical directions. The method further includes performing wide-angle mapping on the chroma intra prediction mode (intraPredModeC) to obtain a modified intraPredModeC; obtaining an angle parameter for the chroma component based on the modified intraPredModeC; and obtaining predicted samples of the chroma component based on the angle parameter. The method provides the minimum number of entries in the LUT that is used to determine chroma intra prediction mode from the initial chroma intra prediction mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/RU2020/050059, filed on Mar. 24, 2020, which claims priority to U.S.Provisional Application No. 62/822,981, filed on Mar. 24, 2019, thedisclosures of which are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

Embodiments of the present application generally relate to the field ofpicture processing and more particularly to methods of chroma intraprediction in video coding.

BACKGROUND

Video coding (video encoding and decoding) is used in a wide range ofdigital video applications, for example broadcast digital TV, videotransmission over internet and mobile networks, real-time conversationalapplications such as video chat, video conferencing, DVD and Blu-raydiscs, video content acquisition and editing systems, and camcorders ofsecurity applications.

The amount of video data needed to depict even a relatively short videocan be substantial, which may result in difficulties when the data is tobe streamed or otherwise communicated across a communications networkwith limited bandwidth capacity. Thus, video data is generallycompressed before being communicated across modern daytelecommunications networks. The size of a video could also be an issuewhen the video is stored on a storage device because memory resourcesmay be limited. Video compression devices often use software and/orhardware at the source to code the video data prior to transmission orstorage, thereby decreasing the quantity of data needed to representdigital video images. The compressed data is then received at thedestination by a video decompression device that decodes the video data.With limited network resources and ever increasing demands of highervideo quality, improved compression and decompression techniques thatimprove compression ratio with little to no sacrifice in picture qualityare desirable.

SUMMARY

Embodiments of the present application provide apparatuses and methodsfor encoding and decoding according to the independent claims.

The foregoing and other objects are achieved by the subject matter ofthe independent claims. Further embodiments are apparent from thedependent claims, the description and the figures.

According to a first aspect, a method of directional intra predictionfor chroma component of a picture is provided. The method includesobtaining an initial intra prediction mode of the chroma component (forexample, mode X in process map422), and deriving a chroma intraprediction mode (intraPredModeC) (for example, mode Y in process map422)from a look up table (LUT) by using the initial intra prediction mode ofthe chroma component, where the chroma component has differentsubsampling ratios in horizontal and vertical directions. The methodfurther includes performing wide-angle mapping on the chroma intraprediction mode (intraPredModeC) to obtain a modified intraPredModeC;obtaining an intraPredAngle parameter for the chroma component based onthe modified intraPredModeC; and obtaining predicted samples of thechroma component based on the intraPredAngle parameter.

In an embodiment, the method further comprises:

-   -   obtaining the value of a luma intra prediction mode        (IntraPredModeY) from a bitstream;    -   wherein the obtaining the initial intra prediction mode of the        chroma component comprises:    -   obtaining the initial intra prediction mode of the chroma        component based on the value of the luma intra prediction mode        (IntraPredModeY).

In an embodiment, the performing wide-angle mapping on the chroma intraprediction mode (intraPredModeC) to obtain the modified intraPredModeCcomprises:

-   -   performing wide-angle mapping on an original intra prediction        mode (predModeIntra) to obtain a modified predModeIntra, wherein        the value of the original predModeIntra is equal to the value of        the chroma intra prediction mode (intraPredModeC).

In an embodiment, the LUT (for example, table 8-4) has 67 entries, theindex for the LUT is 0-66.

The method according to the first aspect can be performed by the deviceaccording to a second aspect of the disclosure. The device ofdirectional intra prediction for chroma component of a picture,comprising an obtaining unit, a deriving unit, and the mapping unit. Theobtaining unit, configured to obtain an initial intra prediction mode ofthe chroma component. The deriving unit, configured to derive a chromaintra prediction mode (intraPredModeC) from a look up table (LUT) byusing the initial intra prediction mode of the chroma component, thechroma component having different subsampling ratios in horizontal andvertical directions. The mapping unit, configured to perform wide-anglemapping on the chroma intra prediction mode (intraPredModeC) to obtain amodified intraPredModeC; and the obtaining unit, further configured toobtain an intraPredAngle parameter for the chroma component based on themodified intraPredModeC; and obtain predicted samples of the chromacomponent based on the intraPredAngle parameter.

Further features and embodiments of the method according to the secondaspect correspond to the features and embodiments of the apparatusaccording to the first aspect.

According to a third aspect, an apparatus for decoding a video streamthat includes a processor and a memory is provided. The memory isstoring instructions that cause the processor to perform the methodaccording to the first aspect.

According to a fourth aspect, an apparatus for encoding a video streamthat includes a processor and a memory is provided. The memory isstoring instructions that cause the processor to perform the methodaccording to the first aspect.

According to a fifth aspect, a computer-readable storage medium havingstored thereon instructions, which when executed, cause one or moreprocessors configured to code video data is proposed. The instructionscause the one or more processors to perform a method according to thefirst aspect or any embodiment of the first aspect.

According to a sixth aspect, a computer program is provided, where thecomputer program comprises program code for performing the methodaccording to the first aspect or any embodiment of the first aspect whenexecuted on a computer.

According to a seventh aspect, the present disclosure further providesan encoder, comprising processing circuitry for carrying out the methodas described above.

According to an eighth aspect, the present disclosure further provides adecoder comprising processing circuitry for carrying out the method asdescribed above.

The embodiments of the present disclosure provide the minimum number ofentries in the LUT that is used to determine chroma intra predictionmode from the initial chroma intra prediction mode. The initial chromaintra prediction mode may be equal to the initial luma intra predictionmode. This is achieved by the order of operations performed, i.e., bychrominance intra prediction mode mapping to luminance mode beingperformed prior to wide-angular mapping.

Details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the disclosure are described in moredetail with reference to the attached figures and drawings, in which:

FIG. 1A is a block diagram showing an example of a video coding systemaccording to an embodiment;

FIG. 1B is a block diagram showing another example of a video codingsystem according to an embodiment;

FIG. 2 is a block diagram showing an example of a video encoderaccording to an embodiment;

FIG. 3 is a block diagram showing an example structure of a videodecoder according to an embodiment;

FIG. 4 is a block diagram illustrating an example of an encodingapparatus or a decoding apparatus;

FIG. 5 is a block diagram illustrating another example of an encodingapparatus or a decoding apparatus;

FIG. 6 is a drawing showing angular intra prediction directions and theassociated intra-prediction modes in VTM-4.0 and VVC specification draftv.4;

FIG. 7 is a drawing showing luma and chroma color planes for YUV 4:2:0and YUV 4:2:2 chroma formats;

FIG. 8 shows an example of the case when IntraPredModeC is derived fromIntraPredModeY where IntraPredModeY is wide-angle intra prediction modeand IntraPredModeC is a non-wide-angle angle intra prediction mode;

FIG. 9 shows an example of the case when IntraPredModeC is derived fromIntraPredModeY where IntraPredModeY is non-wide-angle intra predictionmode and IntraPredModeC is a non-wide-angle angle intra prediction mode;

FIG. 10 shows an example of the case when IntraPredModeC is derived fromIntraPredModeY where IntraPredModeY is non-wide-angle intra predictionmode and IntraPredModeC is a wide-angle angle intra prediction mode;

FIG. 11 shows an example of the case when IntraPredModeC is derived fromIntraPredModeY using prediction mode clipping and where IntraPredModeYis non-wide-angle intra prediction mode and IntraPredModeC is anon-wide-angle angle intra prediction mode;

FIG. 12A is a block diagram illustrating a system for intra predictionof a chroma component according to an embodiment;

FIG. 12B is another block diagram illustrating a system for intraprediction of a chroma component according to an embodiment;

FIG. 13 is a flow diagram illustrating a process of intra prediction ofa chroma component according to an embodiment;

FIG. 14 is a block diagram illustrating a device of intra prediction ofa chroma component according to an embodiment;

FIG. 15 is a block diagram showing an example structure of a contentsupply system which realizes a content delivery service; and

FIG. 16 is a block diagram showing a structure of an example of aterminal device.

In the following identical reference signs refer to identical or atleast functionally equivalent features if not explicitly specifiedotherwise.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanyingfigures, which form part of the disclosure, and which show, by way ofillustration, specific aspects of embodiments of the disclosure orspecific aspects in which embodiments of the present disclosure may beused. It is understood that embodiments of the disclosure may be used inother aspects and comprise structural or logical changes not depicted inthe figures. The following detailed description, therefore, is not to betaken in a limiting sense, and the scope of the present disclosure isdefined by the appended claims.

For instance, it is understood that a disclosure in connection with adescribed method may also hold true for a corresponding device or systemconfigured to perform the method and vice versa. For example, if one ora plurality of specific method steps are described, a correspondingdevice may include one or a plurality of units, e.g. functional units,to perform the described one or plurality of method steps (e.g. one unitperforming the one or plurality of steps, or a plurality of units eachperforming one or more of the plurality of steps), even if such one ormore units are not explicitly described or illustrated in the figures.On the other hand, for example, if a specific apparatus is describedbased on one or a plurality of units, e.g. functional units, acorresponding method may include one step to perform the functionalityof the one or plurality of units (e.g. one step performing thefunctionality of the one or plurality of units, or a plurality of stepseach performing the functionality of one or more of the plurality ofunits), even if such one or plurality of steps are not explicitlydescribed or illustrated in the figures. Further, it is understood thatthe features of the various exemplary embodiments and/or aspectsdescribed herein may be combined with each other, unless specificallynoted otherwise.

Video coding typically refers to the processing of a sequence ofpictures, which form the video or video sequence. Instead of the term“picture” the term “frame” or “image” may be used as synonyms in thefield of video coding. Video coding (or coding in general) comprises twoparts video encoding and video decoding. Video encoding is performed atthe source side, typically comprising processing (e.g. by compression)the original video pictures to reduce the amount of data required forrepresenting the video pictures (for more efficient storage and/ortransmission). Video decoding is performed at the destination side andtypically comprises the inverse processing compared to the encoder toreconstruct the video pictures. Embodiments referring to “coding” ofvideo pictures (or pictures in general) shall be understood to relate to“encoding” or “decoding” of video pictures or respective videosequences. The combination of the encoding part and the decoding part isalso referred to as coding and decoding (CODEC).

In case of lossless video coding, the original video pictures can bereconstructed, i.e. the reconstructed video pictures have the samequality as the original video pictures (assuming no transmission loss orother data loss during storage or transmission). In case of lossy videocoding, further compression, e.g. by quantization, is performed, toreduce the amount of data representing the video pictures, which cannotbe completely reconstructed at the decoder, i.e. the quality of thereconstructed video pictures is lower or worse compared to the qualityof the original video pictures.

Several video coding standards belong to the group of “lossy hybridvideo codecs” (i.e. combine spatial and temporal prediction in thesample domain and 2D transform coding for applying quantization in thetransform domain). Each picture of a video sequence is typicallypartitioned into a set of non-overlapping blocks and the coding istypically performed on a block level. In other words, at the encoder thevideo is typically processed, i.e. encoded, on a block (video block)level, e.g. by using spatial (intra picture) prediction and/or temporal(inter picture) prediction to generate a prediction block, subtractingthe prediction block from the current block (block currentlyprocessed/to be processed) to obtain a residual block, transforming theresidual block and quantizing the residual block in the transform domainto reduce the amount of data to be transmitted (compression), whereas atthe decoder the inverse processing compared to the encoder is applied tothe encoded or compressed block to reconstruct the current block forrepresentation. Furthermore, the encoder duplicates the decoderprocessing loop such that both will generate identical predictions (e.g.intra- and inter predictions) and/or re-constructions for processing,i.e. coding, the subsequent blocks.

In the following embodiments of a video coding system 10, a videoencoder 20 and a video decoder 30 are described based on FIGS. 1 to 3 .

FIG. 1A is a schematic block diagram illustrating an example codingsystem 10, e.g., a video coding system, that may utilize techniques ofthis present application. Video encoder (or encoder) 20 and videodecoder (or decoder) 30 of coding system 10 represent examples ofdevices that may be configured to perform techniques in accordance withvarious examples described in the present application.

As shown in FIG. 1A, the coding system 10 comprises a source device 12configured to provide encoded picture data 21, e.g., to a destinationdevice 14, for decoding the encoded picture data 13.

The source device 12 comprises an encoder 20, and may additionallycomprise a picture source 16, a pre-processor (or pre-processing unit)18, e.g., a picture pre-processor, and a communication interface orcommunication unit 22.

The picture source 16 may comprise or be any kind of picture capturingdevice, for example a camera for capturing a real-world picture, and/orany kind of a picture generating device, for example a computer-graphicsprocessor for generating a computer animated picture, or any kind ofother device for obtaining and/or providing a real-world picture, acomputer generated picture (e.g. a screen content, a virtual reality(VR) picture) and/or any combination thereof (e.g. an augmented reality(AR) picture). The picture source may be any kind of memory or storagestoring any of the aforementioned pictures.

In distinction to the pre-processor 18 and the processing performed bythe pre-processing unit 18, the picture or picture data 17 may also bereferred to as raw picture or raw picture data.

Pre-processor 18 is configured to receive the picture data 17 and toperform pre-processing on the picture data 17 to obtain a pre-processedpicture 19 or pre-processed picture data 19. Pre-processing performed bythe pre-processor 18 may, e.g., comprise trimming, color formatconversion (e.g. from RGB to YCbCr), color correction, or de-noising. Itcan be understood that the pre-processing unit 18 may be optionalcomponent.

The video encoder 20 is configured to receive the pre-processed picturedata 19 and provide encoded picture data 21 (further details will bedescribed below, e.g., based on FIG. 2 ). Communication interface 22 ofthe source device 12 may be configured to receive the encoded picturedata 21 and to transmit the encoded picture data 21 (or any furtherprocessed version thereof) over communication channel 13 to anotherdevice, e.g. the destination device 14 or any other device, for storageor direct reconstruction.

The destination device 14 comprises a decoder 30 (e.g. a video decoder),and may additionally comprise a communication interface or communicationunit 28, a post-processor (or post-processing unit) 32 and a displaydevice 34.

The communication interface 28 of the destination device 14 isconfigured receive the encoded picture data 21 (or any further processedversion thereof), e.g., directly from the source device 12 or from anyother source, e.g., a storage device, such as an encoded picture datastorage device, and provide the encoded picture data 21 to the decoder30.

The communication interface 22 and the communication interface 28 may beconfigured to transmit or receive the encoded picture data 21 or encodeddata 13 via a direct communication link between the source device 12 andthe destination device 14, e.g. a direct wired or wireless connection,or via any kind of network, e.g. a wired or wireless network or anycombination thereof, or any kind of private and public network, or anykind of combination thereof.

The communication interface 22 may be, e.g., configured to package theencoded picture data 21 into an appropriate format, e.g. packets, and/orprocess the encoded picture data using any kind of transmission encodingor processing for transmission over a communication link orcommunication network.

The communication interface 28, forming the counterpart of thecommunication interface 22, may be, e.g., configured to receive thetransmitted data and process the transmission data using any kind ofcorresponding transmission decoding or processing and/or de-packaging toobtain the encoded picture data 21.

Both, communication interface 22 and communication interface 28 may beconfigured as unidirectional communication interfaces as indicated bythe arrow for the communication channel 13 in FIG. 1A pointing from thesource device 12 to the destination device 14, or bi-directionalcommunication interfaces, and may be configured, e.g. to send andreceive messages, e.g. to set up a connection, to acknowledge andexchange any other information related to the communication link and/ordata transmission, e.g. encoded picture data transmission.

The decoder 30 is configured to receive the encoded picture data 21 andprovide decoded picture data 31 or a decoded picture 31 (further detailswill be described below, e.g., based on FIG. 3 or FIG. 5 ).

The post-processor 32 of destination device 14 is configured topost-process the decoded picture data 31 (also called reconstructedpicture data), e.g. the decoded picture 31, to obtain post-processedpicture data 33, e.g. a post-processed picture 33. The post-processingperformed by the post-processing unit 32 may comprise, e.g. color formatconversion (e.g. from YCbCr to RGB), color correction, trimming, orre-sampling, or any other processing, e.g. for preparing the decodedpicture data 31 for display, e.g. by display device 34.

The display device 34 of the destination device 14 is configured toreceive the post-processed picture data 33 for displaying the picture,e.g. to a user or viewer. The display device 34 may be or comprise anykind of display for representing the reconstructed picture, e.g. anintegrated or external display or monitor. The displays may, e.g.comprise liquid crystal displays (LCD), organic light emitting diodes(OLED) displays, plasma displays, projectors, micro LED displays, liquidcrystal on silicon (LCoS), digital light processor (DLP) or any kind ofother display.

Although FIG. 1A depicts the source device 12 and the destination device14 as separate devices, embodiments of devices may also comprise both orboth functionalities, the source device 12 or correspondingfunctionality and the destination device 14 or correspondingfunctionality. In such embodiments the source device 12 or correspondingfunctionality and the destination device 14 or correspondingfunctionality may be implemented using the same hardware and/or softwareor by separate hardware and/or software or any combination thereof.

As will be apparent for the skilled person based on the description, theexistence and (exact) split of functionalities of the different units orfunctionalities within the source device 12 and/or destination device 14as shown in FIG. 1A may vary depending on the actual device andapplication.

The encoder 20 (e.g. a video encoder) or the decoder 30 (e.g. a videodecoder) or both encoder 20 and decoder 30 may be implemented viaprocessing circuitry as shown in FIG. 1B, such as one or moremicroprocessors, digital signal processors (DSPs), application-specificintegrated circuits (ASICs), field-programmable gate arrays (FPGAs),discrete logic, hardware, video coding dedicated or any combinationsthereof. The encoder 20 may be implemented via processing circuitry 46to embody the various modules as discussed with respect to encoder 20 ofFIG. 2 and/or any other encoder system or subsystem described herein.The decoder 30 may be implemented via processing circuitry 46 to embodythe various modules as discussed with respect to decoder 30 of FIG. 3and/or any other decoder system or subsystem described herein. Theprocessing circuitry may be configured to perform the various operationsas discussed later. As shown in FIG. 5 , if the techniques areimplemented partially in software, a device may store instructions forthe software in a suitable, non-transitory computer-readable storagemedium and may execute the instructions in hardware using one or moreprocessors to perform the techniques of this disclosure. Either of videoencoder 20 and video decoder 30 may be integrated as part of a combinedencoder/decoder (CODEC) in a single device, for example, as shown inFIG. 1B.

Source device 12 and destination device 14 may comprise any of a widerange of devices, including any kind of handheld or stationary devices,e.g. notebook or laptop computers, mobile phones, smart phones, tabletsor tablet computers, cameras, desktop computers, set-top boxes,televisions, display devices, digital media players, video gamingconsoles, video streaming devices (such as content services servers orcontent delivery servers), broadcast receiver device, broadcasttransmitter device, or the like and may use no or any kind of operatingsystem. In some cases, the source device 12 and the destination device14 may be equipped for wireless communication. Thus, the source device12 and the destination device 14 may be wireless communication devices.

In some embodiments, video coding system 10 illustrated in FIG. 1A ismerely an example and the techniques of the present application mayapply to video coding settings (e.g., video encoding or video decoding)that do not necessarily include any data communication between theencoding and decoding devices. In other examples, data is retrieved froma local memory, streamed over a network, or the like. A video encodingdevice may encode and store data to memory, and/or a video decodingdevice may retrieve and decode data from memory. In some examples, theencoding and decoding is performed by devices that do not communicatewith one another, but simply encode data to memory and/or retrieve anddecode data from memory.

For convenience of description, embodiments of the disclosure aredescribed herein, for example, by reference to High-Efficiency VideoCoding (HEVC) or to the reference software of Versatile Video coding(VVC), the next generation video coding standard developed by the JointCollaboration Team on Video Coding (JCT-VC) of ITU-T Video CodingExperts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG).One of ordinary skill in the art will understand that embodiments of thedisclosure are not limited to HEVC or VVC.

Encoder and Encoding Method

FIG. 2 shows a schematic block diagram of an example video encoderaccording to an embodiment. In the example of FIG. 2 , video encoder 20comprises an input (or input interface) 201, a residual calculation unit204, a transform processing unit 206, a quantization unit 208, aninverse quantization unit 210, and inverse transform processing unit212, a reconstruction unit 214, a loop filter unit 220, a decodedpicture buffer (DPB) 230, a mode selection unit 260, an entropy encodingunit 270 and an output (or output interface) 272. The mode selectionunit 260 may include an inter prediction unit 244, an intra predictionunit 254 and a partitioning unit 262. Inter prediction unit 244 mayinclude a motion estimation unit and a motion compensation unit (notshown). A video encoder 20 as shown in FIG. 2 may also be referred to ashybrid video encoder or a video encoder according to a hybrid videocodec.

The residual calculation unit 204, the transform processing unit 206,the quantization unit 208, the mode selection unit 260 may be referredto as forming a forward signal path of the encoder 20, whereas theinverse quantization unit 210, the inverse transform processing unit212, the reconstruction unit 214, the buffer 216, the loop filter 220,the decoded picture buffer (DPB) 230, the inter prediction unit 244 andthe intra-prediction unit 254 may be referred to as forming a backwardsignal path of the video encoder 20, wherein the backward signal path ofthe video encoder 20 corresponds to the signal path of the decoder (seevideo decoder 30 in FIG. 3 ). The inverse quantization unit 210, theinverse transform processing unit 212, the reconstruction unit 214, theloop filter 220, the decoded picture buffer (DPB) 230, the interprediction unit 244 and the intra-prediction unit 254 are also referredto forming the “built-in decoder” of video encoder 20.

Pictures & Picture Partitioning (Pictures & Blocks)

The encoder 20 may be configured to receive, e.g. via input 201, apicture (or picture data) 17, e.g. picture of a sequence of picturesforming a video or video sequence. The received picture or picture datamay also be a pre-processed picture (or pre-processed picture data) 19.For sake of simplicity the following description refers to the picture17. The picture 17 may also be referred to as current picture or pictureto be coded (in particular in video coding to distinguish the currentpicture from other pictures, e.g. previously encoded and/or decodedpictures of the same video sequence, i.e. the video sequence which alsocomprises the current picture).

A (digital) picture is or can be regarded as a two-dimensional array ormatrix of samples with intensity values. A sample in the array may alsobe referred to as pixel (short form of picture element) or a pel. Thenumber of samples in horizontal and vertical direction (or axis) of thearray or picture define the size and/or resolution of the picture. Forrepresentation of color, typically three color components are employed,i.e. the picture may be represented or include three sample arrays. InRBG format or color space a picture comprises a corresponding red, greenand blue sample array. However, in video coding each pixel is typicallyrepresented in a luminance and chrominance format or color space, e.g.YCbCr, which comprises a luminance component indicated by Y (sometimesalso L is used instead) and two chrominance components indicated by Cband Cr. The luminance (or short luma) component Y represents thebrightness or grey level intensity (e.g. like in a grey-scale picture),while the two chrominance (or short chroma) components Cb and Crrepresent the chromaticity or color information components. Accordingly,a picture in YCbCr format comprises a luminance sample array ofluminance sample values (Y), and two chrominance sample arrays ofchrominance values (Cb and Cr). Pictures in RGB format may be convertedor transformed into YCbCr format and vice versa, the process is alsoknown as color transformation or conversion. If a picture is monochrome,the picture may comprise only a luminance sample array. Accordingly, apicture may be, for example, an array of luma samples in monochromeformat or an array of luma samples and two corresponding arrays ofchroma samples in 4:2:0, 4:2:2, and 4:4:4 colour format.

Embodiments of the video encoder 20 may comprise a picture partitioningunit (not depicted in FIG. 2 ) configured to partition the picture 17into a plurality of (typically non-overlapping) picture blocks 203.These blocks may also be referred to as root blocks, macro blocks(H.264/AVC) or coding tree blocks (CTB) or coding tree units (CTU)(H.265/HEVC and VVC). The picture partitioning unit may be configured touse the same block size for all pictures of a video sequence and thecorresponding grid defining the block size, or to change the block sizebetween pictures or subsets or groups of pictures, and partition eachpicture into the corresponding blocks.

In some embodiments, the video encoder may be configured to receivedirectly a block 203 of the picture 17, e.g. one, several or all blocksforming the picture 17. The picture block 203 may also be referred to ascurrent picture block or picture block to be coded.

Like the picture 17, the picture block 203 again is or can be regardedas a two-dimensional array or matrix of samples with intensity values(sample values), although of smaller dimension than the picture 17. Inother words, the block 203 may comprise, e.g., one sample array (e.g. aluma array in case of a monochrome picture 17, or a luma or chroma arrayin case of a color picture) or three sample arrays (e.g. a luma and twochroma arrays in case of a color picture 17) or any other number and/orkind of arrays depending on the color format applied. The number ofsamples in horizontal and vertical direction (or axis) of the block 203define the size of block 203. Accordingly, a block may, for example, anM×N (M-column by N-row) array of samples, or an M×N array of transformcoefficients.

Embodiments of the video encoder 20 as shown in FIG. 2 may be configuredto encode the picture 17 block by block, e.g. the encoding andprediction is performed per block 203.

Embodiments of the video encoder 20 as shown in FIG. 2 may be furtherconfigured to partition and/or encode the picture by using slices (alsoreferred to as video slices), wherein a picture may be partitioned intoor encoded using one or more slices (typically non-overlapping), andeach slice may comprise one or more blocks (e.g. CTUs).

Embodiments of the video encoder 20 as shown in FIG. 2 may be furtherconfigured to partition and/or encode the picture by using tile groups(also referred to as video tile groups) and/or tiles (also referred toas video tiles), wherein a picture may be partitioned into or encodedusing one or more tile groups (typically non-overlapping), and each tilegroup may comprise, e.g. one or more blocks (e.g. CTUs) or one or moretiles, wherein each tile, e.g. may be of rectangular shape and maycomprise one or more blocks (e.g. CTUs), e.g. complete or fractionalblocks.

Residual Calculation

The residual calculation unit 204 may be configured to calculate aresidual block 205 (also referred to as residual 205) based on thepicture block 203 and a prediction block 265 (further details about theprediction block 265 are provided later), e.g. by subtracting samplevalues of the prediction block 265 from sample values of the pictureblock 203, sample by sample (pixel by pixel) to obtain the residualblock 205 in the sample domain.

Transform

The transform processing unit 206 may be configured to apply atransform, e.g. a discrete cosine transform (DCT) or discrete sinetransform (DST), on the sample values of the residual block 205 toobtain transform coefficients 207 in a transform domain. The transformcoefficients 207 may also be referred to as transform residualcoefficients and represent the residual block 205 in the transformdomain.

The transform processing unit 206 may be configured to apply integerapproximations of DCT/DST, such as the transforms specified forH.265/HEVC. Compared to an orthogonal DCT transform, such integerapproximations are typically scaled by a certain factor. In order topreserve the norm of the residual block which is processed by forwardand inverse transforms, additional scaling factors are applied as partof the transform process. The scaling factors are typically chosen basedon certain constraints like scaling factors being a power of two forshift operations, bit depth of the transform coefficients, tradeoffbetween accuracy and implementation costs, etc. Specific scaling factorsare, for example, specified for the inverse transform, e.g. by inversetransform processing unit 212 (and the corresponding inverse transform,e.g. by inverse transform processing unit 312 at video decoder 30) andcorresponding scaling factors for the forward transform, e.g. bytransform processing unit 206, at an encoder 20 may be specifiedaccordingly.

Embodiments of the video encoder 20 (respectively transform processingunit 206) may be configured to output transform parameters, e.g. a typeof transform or transforms, e.g. directly or encoded or compressed viathe entropy encoding unit 270, so that, e.g., the video decoder 30 mayreceive and use the transform parameters for decoding.

Quantization

The quantization unit 208 may be configured to quantize the transformcoefficients 207 to obtain quantized coefficients 209, e.g. by applyingscalar quantization or vector quantization. The quantized coefficients209 may also be referred to as quantized transform coefficients 209 orquantized residual coefficients 209.

The quantization process may reduce the bit depth associated with someor all of the transform coefficients 207. For example, an n-bittransform coefficient may be rounded down to an m-bit Transformcoefficient during quantization, where n is greater than m. The degreeof quantization may be modified by adjusting a quantization parameter(QP). For example, for scalar quantization, different scaling may beapplied to achieve finer or coarser quantization. Smaller quantizationstep sizes correspond to finer quantization, whereas larger quantizationstep sizes correspond to coarser quantization. The applicablequantization step size may be indicated by a quantization parameter(QP). The quantization parameter may for example be an index to apredefined set of applicable quantization step sizes. For example, smallquantization parameters may correspond to fine quantization (smallquantization step sizes) and large quantization parameters maycorrespond to coarse quantization (large quantization step sizes) orvice versa. The quantization may include division by a quantization stepsize and a corresponding and/or the inverse dequantization, e.g. byinverse quantization unit 210, may include multiplication by thequantization step size. Embodiments according to some standards, e.g.HEVC, may be configured to use a quantization parameter to determine thequantization step size. Generally, the quantization step size may becalculated based on a quantization parameter using a fixed pointapproximation of an equation including division. Additional scalingfactors may be introduced for quantization and dequantization to restorethe norm of the residual block, which might get modified because of thescaling used in the fixed point approximation of the equation forquantization step size and quantization parameter. In an embodiment, thescaling of the inverse transform and dequantization might be combined.Alternatively, customized quantization tables may be used and signaledfrom an encoder to a decoder, e.g. in a bitstream. The quantization is alossy operation, wherein the loss increases with increasing quantizationstep sizes.

Embodiments of the video encoder 20 (respectively quantization unit 208)may be configured to output quantization parameters (QP), e.g. directlyor encoded via the entropy encoding unit 270, so that, e.g., the videodecoder 30 may receive and apply the quantization parameters fordecoding.

Inverse Quantization

The inverse quantization unit 210 is configured to apply the inversequantization of the quantization unit 208 on the quantized coefficientsto obtain dequantized coefficients 211, e.g. by applying the inverse ofthe quantization scheme applied by the quantization unit 208 based on orusing the same quantization step size as the quantization unit 208. Thedequantized coefficients 211 may also be referred to as dequantizedresidual coefficients 211 and correspond—although typically notidentical to the transform coefficients due to the loss byquantization—to the transform coefficients 207.

Inverse Transform

The inverse transform processing unit 212 is configured to apply theinverse transform of the transform applied by the transform processingunit 206, e.g. an inverse discrete cosine transform (DCT) or inversediscrete sine transform (DST) or other inverse transforms, to obtain areconstructed residual block 213 (or corresponding dequantizedcoefficients 213) in the sample domain. The reconstructed residual block213 may also be referred to as transform block 213.

Reconstruction

The reconstruction unit 214 (e.g. adder or summer 214) is configured toadd the transform block 213 (i.e. reconstructed residual block 213) tothe prediction block 265 to obtain a reconstructed block 215 in thesample domain, e.g. by adding—sample by sample−the sample values of thereconstructed residual block 213 and the sample values of the predictionblock 265.

Filtering

The loop filter unit (or loop filter) 220 is configured to filter thereconstructed block 215 to obtain a filtered block 221, or in general,to filter reconstructed samples to obtain filtered samples. The loopfilter unit is, e.g., configured to smooth pixel transitions, orotherwise improve the video quality. The loop filter unit 220 maycomprise one or more loop filters such as a de-blocking filter, asample-adaptive offset (SAO) filter or one or more other filters, e.g. abilateral filter, an adaptive loop filter (ALF), a sharpening, asmoothing filter or a collaborative filter, or any combination thereof.Although the loop filter unit 220 is shown in FIG. 2 as being an in loopfilter, in other configurations, the loop filter unit 220 may beimplemented as a post loop filter. The filtered block 221 may also bereferred to as filtered reconstructed block.

Embodiments of the video encoder 20 (respectively loop filter unit 220)may be configured to output loop filter parameters (such as sampleadaptive offset information), e.g. directly or encoded via the entropyencoding unit 270, so that, e.g., a decoder 30 may receive and apply thesame loop filter parameters or respective loop filters for decoding.

Decoded Picture Buffer

The decoded picture buffer (DPB) 230 may be a memory that storesreference pictures, or in general reference picture data, for encodingvideo data by video encoder 20. The DPB 230 may be formed by any of avariety of memory devices, such as dynamic random access memory (DRAM),including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. The decodedpicture buffer (DPB) 230 may be configured to store one or more filteredblocks 221. The decoded picture buffer 230 may be further configured tostore other previously filtered blocks, e.g. previously reconstructedand filtered blocks 221, of the same current picture or of differentpictures, e.g. previously reconstructed pictures, and may providecomplete previously reconstructed, i.e. decoded, pictures (andcorresponding reference blocks and samples) and/or a partiallyreconstructed current picture (and corresponding reference blocks andsamples), for example for inter prediction. The decoded picture buffer(DPB) 230 may be also configured to store one or more unfilteredreconstructed blocks 215, or in general unfiltered reconstructedsamples, e.g. if the reconstructed block 215 is not filtered by loopfilter unit 220, or any other further processed version of thereconstructed blocks or samples.

Mode Selection (Partitioning & Prediction)

The mode selection unit 260 comprises partitioning unit 262,inter-prediction unit 244 and intra-prediction unit 254, and isconfigured to receive or obtain original picture data, e.g. an originalblock 203 (current block 203 of the current picture 17), andreconstructed picture data, e.g. filtered and/or unfilteredreconstructed samples or blocks of the same (current) picture and/orfrom one or a plurality of previously decoded pictures, e.g. fromdecoded picture buffer 230 or other buffers (e.g. line buffer, notshown) . . . The reconstructed picture data is used as reference picturedata for prediction, e.g. inter-prediction or intra-prediction, toobtain a prediction block (or predictor) 265.

Mode selection unit 260 may be configured to determine or select apartitioning for a current block prediction mode (including nopartitioning) and a prediction mode (e.g. an intra or inter predictionmode) and generate a corresponding prediction block 265, which is usedfor the calculation of the residual block 205 and for the reconstructionof the reconstructed block 215.

Embodiments of the mode selection unit 260 may be configured to selectthe partitioning and the prediction mode (e.g. from those supported byor available for mode selection unit 260), which provide the best matchor in other words the minimum residual (minimum residual means bettercompression for transmission or storage), or a minimum signalingoverhead (minimum signaling overhead means better compression fortransmission or storage), or which considers or balances both. The modeselection unit 260 may be configured to determine the partitioning andprediction mode based on rate distortion optimization (RDO), i.e. selectthe prediction mode which provides a minimum rate distortion. Terms like“best”, “minimum”, “optimum” etc. in this context do not necessarilyrefer to an overall “best”, “minimum”, “optimum”, etc. but may alsorefer to the fulfillment of a termination or selection criterion like avalue exceeding or falling below a threshold or other constraintsleading potentially to a “sub-optimum selection” but reducing complexityand processing time.

In other words, the partitioning unit 262 may be configured to partitionthe block 203 into smaller block partitions or sub-blocks (which formagain blocks), e.g. iteratively using quad-tree-partitioning (QT),binary partitioning (BT) or triple-tree-partitioning (TT) or anycombination thereof, and to perform, e.g., the prediction for each ofthe block partitions or sub-blocks, wherein the mode selection comprisesthe selection of the tree-structure of the partitioned block 203 and theprediction modes are applied to each of the block partitions orsub-blocks.

In the following the partitioning (e.g. by partitioning unit 260) andprediction processing (by inter-prediction unit 244 and intra-predictionunit 254) performed by an example video encoder 20 will be explained inmore detail.

Partitioning

The partitioning unit 262 may partition (or split) a current block 203into smaller partitions, e.g. smaller blocks of square or rectangularsize. These smaller blocks (which may also be referred to as sub-blocks)may be further partitioned into even smaller partitions. This is alsoreferred to tree-partitioning or hierarchical tree-partitioning, whereina root block, e.g. at root tree-level 0 (hierarchy-level 0, depth 0),may be recursively partitioned, e.g. partitioned into two or more blocksof a next lower tree-level, e.g. nodes at tree-level 1 (hierarchy-level1, depth 1), wherein these blocks may be again partitioned into two ormore blocks of a next lower level, e.g. tree-level 2 (hierarchy-level 2,depth 2), etc. until the partitioning is terminated, e.g. because atermination criterion is fulfilled, e.g. a maximum tree depth or minimumblock size is reached. Blocks which are not further partitioned are alsoreferred to as leaf-blocks or leaf nodes of the tree. A tree usingpartitioning into two partitions is referred to as binary-tree (BT), atree using partitioning into three partitions is referred to asternary-tree (TT), and a tree using partitioning into four partitions isreferred to as quad-tree (QT).

As mentioned before, the term “block” as used herein may be a portion,in particular a square or rectangular portion, of a picture. Withreference, for example, to HEVC and VVC, the block may be or correspondto a coding tree unit (CTU), a coding unit (CU), prediction unit (PU),and transform unit (TU) and/or to the corresponding blocks, e.g. acoding tree block (CTB), a coding block (CB), a transform block (TB) orprediction block (PB).

For example, a coding tree unit (CTU) may be or comprise a CTB of lumasamples, two corresponding CTBs of chroma samples of a picture that hasthree sample arrays, or a CTB of samples of a monochrome picture or apicture that is coded using three separate colour planes and syntaxstructures used to code the samples. Correspondingly, a coding treeblock (CTB) may be an N×N block of samples for some value of N such thatthe division of a component into CTBs is a partitioning. A coding unit(CU) may be or comprise a coding block of luma samples, twocorresponding coding blocks of chroma samples of a picture that hasthree sample arrays, or a coding block of samples of a monochromepicture or a picture that is coded using three separate colour planesand syntax structures used to code the samples. Correspondingly a codingblock (CB) may be an M×N block of samples for some values of M and Nsuch that the division of a CTB into coding blocks is a partitioning.

In some embodiments, e.g., according to HEVC, a coding tree unit (CTU)may be split into CUs by using a quad-tree structure denoted as codingtree. The decision whether to code a picture area using inter-picture(temporal) or intra-picture (spatial) prediction is made at the CUlevel. Each CU can be further split into one, two or four PUs accordingto the PU splitting type. Inside one PU, the same prediction process isapplied and the relevant information is transmitted to the decoder on aPU basis. After obtaining the residual block by applying the predictionprocess based on the PU splitting type, a CU can be partitioned intotransform units (TUs) according to another quadtree structure similar tothe coding tree for the CU.

In some embodiments, e.g., according to the latest video coding standardcurrently in development, which is referred to as Versatile Video Coding(VVC), a combined Quad-tree and binary tree (QTBT) partitioning is forexample used to partition a coding block. In the QTBT block structure, aCU can have either a square or rectangular shape. For example, a codingtree unit (CTU) is first partitioned by a quadtree structure. Thequadtree leaf nodes are further partitioned by a binary tree or ternary(or triple) tree structure. The partitioning tree leaf nodes are calledcoding units (CUs), and that segmentation is used for prediction andtransform processing without any further partitioning. This means thatthe CU, PU and TU have the same block size in the QTBT coding blockstructure. In parallel, multiple partition, for example, triple treepartition may be used together with the QTBT block structure.

In one example, the mode selection unit 260 of video encoder 20 may beconfigured to perform any combination of the partitioning techniquesdescribed herein.

As described above, the video encoder 20 is configured to determine orselect the best or an optimum prediction mode from a set of (e.g.pre-determined) prediction modes. The set of prediction modes maycomprise, e.g., intra-prediction modes and/or inter-prediction modes.

Intra-Prediction

The set of intra-prediction modes may comprise 35 differentintra-prediction modes, e.g. non-directional modes like DC (or mean)mode and planar mode, or directional modes, e.g. as defined in HEVC, ormay comprise 67 different intra-prediction modes, e.g. non-directionalmodes like DC (or mean) mode and planar mode, or directional modes, e.g.as defined for VVC.

The intra-prediction unit 254 is configured to use reconstructed samplesof neighboring blocks of the same current picture to generate anintra-prediction block 265 according to an intra-prediction mode of theset of intra-prediction modes.

The intra prediction unit 254 (or in general the mode selection unit260) is further configured to output intra-prediction parameters (or ingeneral information indicative of the selected intra prediction mode forthe block) to the entropy encoding unit 270 in form of syntax elements266 for inclusion into the encoded picture data 21, so that, e.g., thevideo decoder 30 may receive and use the prediction parameters fordecoding.

Inter-Prediction

The set of (or possible) inter-prediction modes depends on the availablereference pictures (i.e. previous at least partially decoded pictures,e.g. stored in DBP 230) and other inter-prediction parameters, e.g.whether the whole reference picture or only a part, e.g. a search windowarea around the area of the current block, of the reference picture isused for searching for a best matching reference block, and/or e.g.whether pixel interpolation is applied, e.g. half/semi-pel and/orquarter-pel interpolation, or not.

Additional to the above prediction modes, skip mode and/or direct modemay be applied.

The inter prediction unit 244 may include a motion estimation (ME) unitand a motion compensation (MC) unit (both not shown in FIG. 2 ). Themotion estimation unit may be configured to receive or obtain thepicture block 203 (current picture block 203 of the current picture 17)and a decoded picture 231, or at least one or a plurality of previouslyreconstructed blocks, e.g. reconstructed blocks of one or a plurality ofother/different previously decoded pictures 231, for motion estimation.E.g., a video sequence may comprise the current picture and thepreviously decoded pictures 231, or in other words, the current pictureand the previously decoded pictures 231 may be part of or form asequence of pictures forming a video sequence.

The encoder 20, for example, may be configured to select a referenceblock from a plurality of reference blocks of the same or differentpictures of the plurality of other pictures and provide a referencepicture (or reference picture index) and/or an offset (spatial offset)between the position (x, y coordinates) of the reference block and theposition of the current block as inter prediction parameters to themotion estimation unit. This offset is also called motion vector (MV).

The motion compensation unit is configured to obtain, e.g. receive, aninter prediction parameter and to perform inter prediction based on orusing the inter prediction parameter to obtain an inter prediction block265. Motion compensation, performed by the motion compensation unit, mayinvolve fetching or generating the prediction block based on themotion/block vector determined by motion estimation, possibly performinginterpolations to sub-pixel precision. Interpolation filtering maygenerate additional pixel samples from known pixel samples, thuspotentially increasing the number of candidate prediction blocks thatmay be used to code a picture block. Upon receiving the motion vectorfor the PU of the current picture block, the motion compensation unitmay locate the prediction block to which the motion vector points in oneof the reference picture lists.

The motion compensation unit may also generate syntax elementsassociated with the blocks and video slices for use by video decoder 30in decoding the picture blocks of the video slice. In addition or as analternative to slices and respective syntax elements, tile groups and/ortiles and respective syntax elements may be generated or used.

Entropy Coding

The entropy encoding unit 270 is configured to apply, for example, anentropy encoding algorithm or scheme (e.g. a variable length coding(VLC) scheme, an context adaptive VLC scheme (CAVLC), an arithmeticcoding scheme, a binarization, a context adaptive binary arithmeticcoding (CABAC), syntax-based context-adaptive binary arithmetic coding(SBAC), probability interval partitioning entropy (PIPE) coding oranother entropy encoding methodology or technique) or bypass (nocompression) on the quantized coefficients 209, inter predictionparameters, intra prediction parameters, loop filter parameters and/orother syntax elements to obtain encoded picture data 21 which can beoutput via the output 272, e.g. in the form of an encoded bitstream 21,so that, e.g., the video decoder 30 may receive and use the parametersfor decoding. The encoded bitstream 21 may be transmitted to videodecoder 30, or stored in a memory for later transmission or retrieval byvideo decoder 30.

Other structural variations of the video encoder 20 can be used toencode the video stream. For example, a non-transform based encoder 20can quantize the residual signal directly without the transformprocessing unit 206 for certain blocks or frames. In another embodiment,an encoder 20 can have the quantization unit 208 and the inversequantization unit 210 combined into a single unit.

Decoder and Decoding Method

FIG. 3 shows an example of a video decoder according to an embodiment.Video decoder 30 is configured to receive encoded picture data 21 (e.g.encoded bitstream), e.g. encoded by encoder 20, to obtain a decodedpicture 331. The encoded picture data or bitstream comprises informationfor decoding the encoded picture data, e.g. data that represents pictureblocks of an encoded video slice (and/or tile groups or tiles) andassociated syntax elements.

In the example of FIG. 3 , the decoder 30 comprises an entropy decodingunit 304, an inverse quantization unit 310, an inverse transformprocessing unit 312, a reconstruction unit 314 (e.g. a summer), a loopfilter 320, a decoded picture buffer (DBP) 330, a mode application unit360, an inter prediction unit 344 and an intra prediction unit 354.Inter prediction unit 344 may be or include a motion compensation unit.Video decoder 30 may, in some examples, perform a decoding passgenerally reciprocal to the encoding pass described with respect tovideo encoder 100 from FIG. 2 .

As explained with regard to the encoder 20, the inverse quantizationunit 210, the inverse transform processing unit 212, the reconstructionunit 214 the loop filter 220, the decoded picture buffer (DPB) 230, theinter prediction unit 344 and the intra prediction unit 354 are alsoreferred to as forming the “built-in decoder” of video encoder 20.Accordingly, the inverse quantization unit 310 may be identical infunction to the inverse quantization unit 110, the inverse transformprocessing unit 312 may be identical in function to the inversetransform processing unit 212, the reconstruction unit 314 may beidentical in function to reconstruction unit 214, the loop filter 320may be identical in function to the loop filter 220, and the decodedpicture buffer 330 may be identical in function to the decoded picturebuffer 230. Therefore, the explanations provided for the respectiveunits and functions of the video 20 encoder apply correspondingly to therespective units and functions of the video decoder 30.

Entropy Decoding

The entropy decoding unit 304 is configured to parse the bitstream 21(or in general encoded picture data) and perform, for example, entropydecoding to the encoded picture data 21 to obtain, e.g., quantizedcoefficients 309 and/or decoded coding parameters (not shown in FIG. 3), e.g. any or all of inter prediction parameters (e.g. referencepicture index and motion vector), intra prediction parameter (e.g. intraprediction mode or index), transform parameters, quantizationparameters, loop filter parameters, and/or other syntax elements.Entropy decoding unit 304 maybe configured to apply the decodingalgorithms or schemes corresponding to the encoding schemes as describedwith regard to the entropy encoding unit 270 of the encoder 20. Entropydecoding unit 304 may be further configured to provide inter predictionparameters, intra prediction parameter and/or other syntax elements tothe mode application unit 360 and other parameters to other units of thedecoder 30. Video decoder 30 may receive the syntax elements at thevideo slice level and/or the video block level. In addition or as analternative to slices and respective syntax elements, tile groups and/ortiles and respective syntax elements may be received and/or used.

Inverse Quantization

The inverse quantization unit 310 may be configured to receivequantization parameters (QP) (or in general information related to theinverse quantization) and quantized coefficients from the encodedpicture data 21 (e.g. by parsing and/or decoding, e.g. by entropydecoding unit 304) and to apply based on the quantization parameters aninverse quantization on the decoded quantized coefficients 309 to obtaindequantized coefficients 311, which may also be referred to as transformcoefficients 311. The inverse quantization process may include use of aquantization parameter determined by video encoder 20 for each videoblock in the video slice (or tile or tile group) to determine a degreeof quantization and, likewise, a degree of inverse quantization thatshould be applied.

Inverse Transform

Inverse transform processing unit 312 may be configured to receivedequantized coefficients 311, also referred to as transform coefficients311, and to apply a transform to the dequantized coefficients 311 inorder to obtain reconstructed residual blocks 213 in the sample domain.The reconstructed residual blocks 213 may also be referred to astransform blocks 313. The transform may be an inverse transform, e.g.,an inverse DCT, an inverse DST, an inverse integer transform, or aconceptually similar inverse transform process. The inverse transformprocessing unit 312 may be further configured to receive transformparameters or corresponding information from the encoded picture data 21(e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304) todetermine the transform to be applied to the dequantized coefficients311.

Reconstruction

The reconstruction unit 314 (e.g. adder or summer 314) may be configuredto add the reconstructed residual block 313, to the prediction block 365to obtain a reconstructed block 315 in the sample domain, e.g. by addingthe sample values of the reconstructed residual block 313 and the samplevalues of the prediction block 365.

Filtering

The loop filter unit 320 (either in the coding loop or after the codingloop) is configured to filter the reconstructed block 315 to obtain afiltered block 321, e.g. to smooth pixel transitions, or otherwiseimprove the video quality. The loop filter unit 320 may comprise one ormore loop filters such as a de-blocking filter, a sample-adaptive offset(SAO) filter or one or more other filters, e.g. a bilateral filter, anadaptive loop filter (ALF), a sharpening, a smoothing filter or acollaborative filter, or any combination thereof. Although the loopfilter unit 320 is shown in FIG. 3 as being an in loop filter, in otherconfigurations, the loop filter unit 320 may be implemented as a postloop filter.

Decoded Picture Buffer

The decoded video blocks 321 of a picture are then stored in decodedpicture buffer 330, which stores the decoded pictures 331 as referencepictures for subsequent motion compensation for other pictures and/orfor output respectively display.

The decoder 30 is configured to output the decoded picture 331, e.g. viaoutput 332, for presentation or viewing to a user.

Prediction

The inter prediction unit 344 may be identical to the inter predictionunit 244 (in particular to the motion compensation unit) and the intraprediction unit 354 may be identical to the inter prediction unit 254 infunction, and performs split or partitioning decisions and predictionbased on the partitioning and/or prediction parameters or respectiveinformation received from the encoded picture data 21 (e.g. by parsingand/or decoding, e.g. by entropy decoding unit 304). Mode applicationunit 360 may be configured to perform the prediction (intra or interprediction) per block based on reconstructed pictures, blocks orrespective samples (filtered or unfiltered) to obtain the predictionblock 365.

When the video slice is coded as an intra coded (I) slice, intraprediction unit 354 of mode application unit 360 is configured togenerate prediction block 365 for a picture block of the current videoslice based on a signaled intra prediction mode and data from previouslydecoded blocks of the current picture. When the video picture is codedas an inter coded (i.e., B, or P) slice, inter prediction unit 344 (e.g.motion compensation unit) of mode application unit 360 is configured toproduce prediction blocks 365 for a video block of the current videoslice based on the motion vectors and other syntax elements receivedfrom entropy decoding unit 304. For inter prediction, the predictionblocks may be produced from one of the reference pictures within one ofthe reference picture lists. Video decoder 30 may construct thereference frame lists, List 0 and List 1, using default constructiontechniques based on reference pictures stored in DPB 330. The same orsimilar may be applied for or by embodiments using tile groups (e.g.video tile groups) and/or tiles (e.g. video tiles) in addition oralternatively to slices (e.g. video slices), e.g. a video may be codedusing I, P or B tile groups and/or tiles.

Mode application unit 360 is configured to determine the predictioninformation for a video block of the current video slice by parsing themotion vectors or related information and other syntax elements, anduses the prediction information to produce the prediction blocks for thecurrent video block being decoded. For example, the mode applicationunit 360 uses some of the received syntax elements to determine aprediction mode (e.g., intra or inter prediction) used to code the videoblocks of the video slice, an inter prediction slice type (e.g., Bslice, P slice, or GPB slice), construction information for one or moreof the reference picture lists for the slice, motion vectors for eachinter encoded video block of the slice, inter prediction status for eachinter coded video block of the slice, and other information to decodethe video blocks in the current video slice. The same or similar may beapplied for or by embodiments using tile groups (e.g. video tile groups)and/or tiles (e.g. video tiles) in addition or alternatively to slices(e.g. video slices), e.g. a video may be coded using I, P or B tilegroups and/or tiles.

Embodiments of the video decoder 30 as shown in FIG. 3 may be configuredto partition and/or decode the picture by using slices (also referred toas video slices), wherein a picture may be partitioned into or decodedusing one or more slices (typically non-overlapping), and each slice maycomprise one or more blocks (e.g. CTUs).

Embodiments of the video decoder 30 as shown in FIG. 3 may be configuredto partition and/or decode the picture by using tile groups (alsoreferred to as video tile groups) and/or tiles (also referred to asvideo tiles), wherein a picture may be partitioned into or decoded usingone or more tile groups (typically non-overlapping), and each tile groupmay comprise, e.g. one or more blocks (e.g. CTUs) or one or more tiles,wherein each tile, e.g. may be of rectangular shape and may comprise oneor more blocks (e.g. CTUs), e.g. complete or fractional blocks.

Other variations of the video decoder 30 can be used to decode theencoded picture data 21. For example, the decoder 30 can produce theoutput video stream without the loop filtering unit 320. For example, anon-transform based decoder 30 can inverse-quantize the residual signaldirectly without the inverse-transform processing unit 312 for certainblocks or frames. In another embodiment, the video decoder 30 can havethe inverse-quantization unit 310 and the inverse-transform processingunit 312 combined into a single unit.

It should be understood that, in the encoder 20 and the decoder 30, aprocessing result of a current step may be further processed and thenoutput to the next step. For example, after interpolation filtering,motion vector derivation or loop filtering, a further operation, such asClip or shift, may be performed on the processing result of theinterpolation filtering, motion vector derivation or loop filtering.

It should be noted that further operations may be applied to the derivedmotion vectors of current block (including but not limit to controlpoint motion vectors of affine mode, sub-block motion vectors in affine,planar, advanced temporal motion vector prediction (ATMVP) modes,temporal motion vectors, and so on). For example, the value of motionvector is constrained to a predefined range according to itsrepresenting bit. If the representing bit of motion vector is bitDepth,then the range is −2{circumflex over ( )}(bitDepth−1)˜2{circumflex over( )}(bitDepth−1)−1, where “{circumflex over ( )}” means exponentiation.For example, if bitDepth is set equal to 16, the range is −32768˜32767;if bitDepth is set equal to 18, the range is −131072˜131071. Forexample, the value of the derived motion vector (e.g. the MVs of four4×4 sub-blocks within one 8×8 block) is constrained such that the maxdifference between integer parts of the four 4×4 sub-block MVs is nomore than N pixels, such as no more than 1 pixel. Here provides twomethods for constraining the motion vector according to the bitDepth.

Method 1: remove the overflow MSB (most significant bit) by flowingoperationsux=(myx+2^(bitDepth))%2^(bitDepth)  (1)mvx=(ux>=2^(bitDepth−1))?(ux−2^(bitDepth)):ux  (2)uy=(mvy+2^(bitDepth))%2^(bitDepth)  (3)mvy=(uy>=2^(bitDepth−1))?(uy−2^(bitDepth)):uy  (4)where mvx is a horizontal component of a motion vector of an image blockor a sub-block, mvy is a vertical component of a motion vector of animage block or a sub-block, and ux and uy indicates an intermediatevalue;

For example, if the value of mvx is −32769, after applying formula (1)and (2), the resulting value is 32767. In computer system, decimalnumbers are stored as two's complement. The two's complement of −32769is 1,0111,1111,1111,1111 (17 bits), then the MSB is discarded, so theresulting two's complement is 0111,1111,1111,1111 (decimal number is32767), which is same as the output by applying formula (1) and (2).ux=(mvpx+mvdx+2^(bitDepth))%2^(bitDepth)  (5)mvx=(ux>=2^(bitDepth−1))?(ux−2^(bitDepth)):ux  (6)uy=(mvpy+mvdy+2^(bitDepth))%2^(bitDepth)  (7)mvy=(uy>=2^(bitDepth−1))?(uy−2^(bitDepth)):uy  (8)

The operations may be applied during the sum of mvp and mvd, as shown informula (5) to (8).

Method 2: remove the overflow MSB by clipping the valuevx=Clip3(−2^(bitDepth−1),2^(bitDepth−1)−1,vx)vy=Clip3(−2^(bitDepth−1),2^(bitDepth−1)−1,vy)

where vx is a horizontal component of a motion vector of an image blockor a sub-block, vy is a vertical component of a motion vector of animage block or a sub-block; x, y and z respectively correspond to threeinput value of the MV clipping process, and the definition of functionClip3 is as follow:

${{Clip}\mspace{14mu} 3\left( {x,y,z} \right)} = \left\{ \begin{matrix}x & ; & {z < x} \\y & ; & {z > y} \\z & ; & {otherwise}\end{matrix} \right.$

FIG. 4 is a schematic diagram of a video coding device 400 according toan embodiment of the disclosure. The video coding device 400 is suitablefor implementing the disclosed embodiments as described herein. In anembodiment, the video coding device 400 may be a decoder such as videodecoder 30 of FIG. 1A or an encoder such as video encoder 20 of FIG. 1A.

The video coding device 400 comprises ingress ports (or input ports) 410and receiver units (Rx) 420 for receiving data; a processor, logic unit,or central processing unit (CPU) 430 to process the data; transmitterunits (Tx) 440 and egress ports (or output ports) 450 for transmittingthe data; and a memory 460 for storing the data. The video coding device400 may also comprise optical-to-electrical (OE) components andelectrical-to-optical (EO) components coupled to the ingress ports 410,the receiver units 420, the transmitter units 440, and the egress ports450 for egress or ingress of optical or electrical signals.

The processor 430 is implemented by hardware and software. The processor430 may be implemented as one or more CPU chips, cores (e.g., as amulti-core processor), FPGAs, ASICs, and DSPs. The processor 430 is incommunication with the ingress ports 410, receiver units 420,transmitter units 440, egress ports 450, and memory 460. The processor430 comprises a coding module 470. The coding module 470 implements thedisclosed embodiments described above. For instance, the coding module470 implements, processes, prepares, or provides the various codingoperations. The inclusion of the coding module 470 therefore provides asubstantial improvement to the functionality of the video coding device400 and effects a transformation of the video coding device 400 to adifferent state. Alternatively, the coding module 470 is implemented asinstructions stored in the memory 460 and executed by the processor 430.

The memory 460 may comprise one or more disks, tape drives, andsolid-state drives and may be used as an over-flow data storage device,to store programs when such programs are selected for execution, and tostore instructions and data that are read during program execution. Thememory 460 may be, for example, volatile and/or non-volatile and may bea read-only memory (ROM), random access memory (RAM), ternarycontent-addressable memory (TCAM), and/or static random-access memory(SRAM).

FIG. 5 is a block diagram of an apparatus that may be used as either orboth of the source device 12 and the destination device 14 from FIG. 1according to an embodiment.

A processor 502 in the apparatus 500 can be a central processing unit.Alternatively, the processor 502 can be any other type of device, ormultiple devices, capable of manipulating or processing informationnow-existing or hereafter developed. Although the disclosed embodimentscan be practiced with a single processor as shown, e.g., the processor502, advantages in speed and efficiency can be achieved using more thanone processor.

A memory 504 in the apparatus 500 can be a read only memory (ROM) deviceor a random access memory (RAM) device in an embodiment. Any othersuitable type of storage device can be used as the memory 504. Thememory 504 can include code and data 506 that is accessed by theprocessor 502 using a bus 512. The memory 504 can further include anoperating system 508 and application programs 510, the applicationprograms 510 including at least one program that permits the processor502 to perform the methods described here. For example, the applicationprograms 510 can include applications 1 through N, which further includea video coding application that performs the methods described here. Theapparatus 500 can also include one or more output devices, such as adisplay 518. The display 518 may be, in one example, a touch sensitivedisplay that combines a display with a touch sensitive element that isoperable to sense touch inputs. The display 518 can be coupled to theprocessor 502 via the bus 512.

Although depicted here as a single bus, the bus 512 of the apparatus 500can be composed of multiple buses. Further, the secondary storage 514can be directly coupled to the other components of the apparatus 500 orcan be accessed via a network and can comprise a single integrated unitsuch as a memory card or multiple units such as multiple memory cards.The apparatus 500 can thus be implemented in a wide variety ofconfigurations.

Directional intra prediction is a well-known technique that includespropagating the values of the neighboring samples into the predictedblock as specified by the prediction direction. FIG. 6 illustrates the93 prediction directions, where the dashed directions are associatedwith the wide-angle modes that are only applied to non-square blocks.

Direction could be specified by the increase of an offset betweenposition of predicted and reference sample. The larger magnitude of thisincrease corresponds to a greater skew of the prediction direction.Table 1 specifies the mapping table between predModeIntra and the angleparameter intraPredAngle. This parameter is in fact the increase of thisoffset per row (or per column) specified in the 1/32 sample resolution.

TABLE 1 Specification of intraPredAngle predModeIntra −14 −13 −12 −11−10 −9 −8 −7 −6 −5 −4 −3 −2 −1 2 3 4 intraPredAngle 512 341 256 171 128102 86 73 64 57 51 45 39 35 32 29 26 predModeIntra 5 6 7 8 9 10 11 12 1314 15 16 17 18 19 20 21 intraPredAngle 23 20 18 16 14 12 10 8 6 4 3 2 10 −1 −2 −3 predModeIntra 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 3738 intraPredAngle −4 −6 −8 −10 −12 −14 −16 −18 −20 −23 −26 −29 −32 −29−26 −23 −20 predModeIntra 39 40 41 42 43 44 45 46 47 48 49 50 51 52 5354 55 intraPredAngle −18 −16 −14 −12 −10 −8 −6 −4 −3 −2 −1 0 1 2 3 4 6predModeIntra 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72intraPredAngle 8 10 12 14 16 18 20 23 26 29 32 35 39 45 51 57 64predModeIntra 73 74 75 76 77 78 79 80 intraPredAngle 73 86 102 128 171256 341 512

Wide-angle modes could be identified by the absolute value ofintraPredAngle greater than 32 (1 sample), that corresponds to the slopeof prediction direction greater than 45 degrees.

Predicted samples (“predSamples”) could be obtained from theneighbouring samples “p” as described below:

The values of the prediction samples predSamples[x][y], with x=0 . . .nTbW−1, y=0 . . . nTbH−1 are derived as follows:

-   -   If predModeIntra is greater than or equal to 34, the following        ordered operations apply:    -   1. The reference sample array ref[x] is specified as follows:        -   The following applies:            ref[x]=p[−1−refIdx+x][−1−refIdx], with x=0 . . . nTbW+refIdx        -   If intraPredAngle is less than 0, the main reference sample            array is extended as follows:            -   When (nTbH*intraPredAngle)>>5 is less than −1,                ref[x]=p[−1−refIdx][−1−refIdx+((x*invAngle+128)>>8)],                with x=−1 . . . (nTbH*intraPredAngle)>>5                ref[((nTbH*intraPredAngle)>>5)−1]=ref[(nTbH*intraPredAngle)>>5]                ref[nTbW+1+refIdx]=ref[nTbW+refIdx]        -   Otherwise,            ref[x]=p[−1−refIdx+x][−1−refIdx], with x=nTbW+1+refIdx . . .            refW+refIdx            ref[−1]=ref[0]            -   The additional samples ref[refW+refIdx+x] with x=1 . . .                (Max(1, nTbW/nTbH)*refIdx+1) are derived as follows:                ref[refW+refIdx+x]=p[−1+refW][−1−refIdx]    -   2. The values of the prediction samples predSamples[x][y], with        x=0 . . . nTbW−1, y=0 . . . nTbH−1 are derived as follows:        -   The index variable iIdx and the multiplication factor iFact            are derived as follows:            iIdx=((y+1+refIdx)*intraPredAngle)>>5+refIdx            iFact=((y+1+refIdx)*intraPredAngle)&31        -   If cIdx is equal to 0, the following applies:            -   The interpolation filter coefficients fT[j] with j=0 . .                . 3 are derived as follows:                fT[j]=filterFlag?fG[iFact][j]:fC[iFact][j]            -   The value of the prediction samples predSamples[x][y] is                derived as follows:                predSamples[x][y]=Clip1Y(((Σ_(i=0) ³                fT[i]*ref[x+iIdx+i])+32)>>6)        -   Otherwise (cIdx is not equal to 0), depending on the value            of iFact, the following applies:            -   If iFact is not equal to 0, the value of the prediction                samples predSamples[x][y] is derived as follows:                predSamples[x][y]=((32−iFact)*ref[x+iIdx+1]+iFact*ref[x+iIdx+2]+16)>>5            -   Otherwise, the value of the prediction samples                predSamples[x][y] is derived as follows:                predSamples[x][y]=ref[x+iIdx+1]    -   Otherwise (predModeIntra is less than 34), the following ordered        operations apply:    -   1. The reference sample array ref[x] is specified as follows:        -   The following applies:            ref[x]=p[−1−refIdx][−1−refIdx+x], with x=0 . . . nTbH+refIdx    -   If intraPredAngle is less than 0, the main reference sample        array is extended as follows:        -   When (nTbW*intraPredAngle)>>5 is less than −1,            ref[x]=p[−1−refIdx+((x*invAngle+128)>>8)][−1−refIdx], with            x=−1 . . . (nTbW*intraPredAngle)>>5            ref[((nTbW*intraPredAngle)>>5)−1]=ref[(nTbW*intraPredAngle)>>5]  (8-145)            ref[nTbG+1+refIdx]=ref[nTbH+refIdx]        -   Otherwise,            ref[x]=p[−1−refIdx][−1−refIdx+x], with x=nTbH+1+refIdx . . .            refH+refIdx            ref[−1]=ref[0]        -   The additional samples ref[refH+refIdx+x] with x=1 . . .            (Max(1, nTbW/nTbH)*refIdx+1) are derived as follows:            ref[refH+refIdx+x]=p[−1+refH][−1−refIdx]    -   2. The values of the prediction samples predSamples[x][y], with        x=0 . . . nTbW−1, y=0 . . . nTbH−1 are derived as follows:        -   The index variable iIdx and the multiplication factor iFact            are derived as follows:            iIdx=((x+1+refIdx)*intraPredAngle)>>5            iFact=((x+1+refIdx)*intraPredAngle)&31        -   If cIdx is equal to 0, the following applies:            -   The interpolation filter coefficients fT[j] with j=0 . .                . 3 are derived as follows:                fT[j]=filterFlag?fG[iFact][j]:fC[iFact][j]            -   The value of the prediction samples predSamples[x][y] is                derived as follows:                predSamples[x][y]=Clip1Y(((Σ_(i=0) ³                fT[i]*ref[y+iIdx+i])+32)>>6)        -   Otherwise (cIdx is not equal to 0), depending on the value            of iFact, the following applies:            -   If iFact is not equal to 0, the value of the prediction                samples predSamples[x][y] is derived as follows:                predSamples[x][y]=((32−iFact)*ref[y+iIdx+1]+iFact*ref[y+iIdx+2]+16)>>5            -   Otherwise, the value of the prediction samples                predSamples[x][y] is derived as follows:                predSamples[x][y]=ref[y+iIdx+1]

Signaling of intra prediction modes for luma and chroma components couldbe performed in such a way, that chroma intra prediction mode is derivedfrom luma intra prediction mode:

The chroma intra prediction mode IntraPredModeC[xCb][yCb] is derivedusing intra_chromapred_mode[xCb][yCb] andIntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2] as specified in Table 2and Table 3.

TABLE 2 Specification of IntraPredModeC[ xCb ][ yCb] depending onintra_chroma_pred_mode[ xCb ][ yCb] and IntraPredModeY[ xCb + cbWidth/2][ yCb + cbHeight/2 ] when sps_cclm_enabled_flag is equal to 0IntraPredModeY[ xCb + intra_chroma_pred_ cbWidth/2 ][ yCb + cbHeight/2 ]mode[ xCb ][ yCb ] 0 50 18 1 X ( 0 <= X <= 66) 0 66 0 0 0 0 1 50 66 5050 50 2 18 18 66 18 18 3 1 1 1 66 1 4 0 50 18 1 X

TABLE 3 Specification of IntraPredModeC[ xCb ][ yCb] depending onintra_chroma_pred_mode[ xCb ][ yCb] and IntraPredModeY[ xCb + cbWidth/2][ yCb + cbHeight/2 ] when sps_cclm_enabled_flag is equal to 1IntraPredModeY[ xCb + intra_chroma_pred_ cbWidth/2 ][ yCb + cbHeight/2 ]mode[ xCb ][ yCb ] 0 50 18 1 X ( 0 <= X <= 66) 0 66 0 0 0 0 1 50 66 5050 50 2 18 18 66 18 18 3 1 1 1 66 1 4 81 81 81 81 81 5 82 82 82 82 82 683 83 83 83 83 7 0 50 18 1 X

Parameter “intra_chromapred_mode” is signaled within a bitstream. FromTable 2 and Table 3 it could be noticed, that in certain cases (denotedby “X”), intra prediction mode for chroma component (IntraPredModeC) isset equal to the intra prediction mode specified for the co-located lumablock.

Chroma format determines precedence and subsampling of chroma arrays, asshown in FIG. 7 . In monochrome sampling there is only one sample array,which is nominally considered the luma array.

In 4:2:0 sampling, each of the two chroma arrays has half the height andhalf the width of the luma array.

In 4:2:2 sampling, each of the two chroma arrays has the same height andhalf the width of the luma array.

This solution provides the same intra prediction direction forpredicting chroma samples as it is specified for luma samples. However,when chroma subsampling ratio in horizontal direction is not equal tochroma subsampling ratio in vertical direction, intra predictiondirections for chroma will be affected by subsampling, resulting indifferent mapping of intra prediction mode to the angle of intraprediction direction. To compensate for this effect, in the rangeextensions of HM it was proposed to perform a mode mapping operation,i.e. to perform a fetch from the dedicated lookup table (LUT) for thecorresponding luma intra prediction mode (IntraPredModeY) and to use thefetched value for chroma intra prediction mode (IntraPredModeC). Table 4gives this LUT for the set of modes specified in the HEVC standard.

TABLE 4 Specification of the LUT for intra prediction mode mapping for4:2:2 chroma format IntraPredModeY 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1516 17 IntraPredModeC 0 1 2 2 2 2 2 4 6 8 10 12 14 16 18 18 18 18IntraPredModeY 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34IntraPredModeC 22 22 23 23 24 24 25 25 26 27 27 28 28 29 29 30 30

In VVC specification draft 4 in the intra prediction process, the indexof intra prediction mode (intraPredMode) is modified in accordance withaspect ratio as follows:

-   -   The variables nW and nH are derived as follows:        -   If IntraSubPartitionsSplitType is equal to ISP_NO_SPLIT or            cIdx is not equal to 0, the following applies:            -   nW=nTbW            -   nH=nTbH        -   Otherwise (IntraSubPartitionsSplitType is not equal to            ISP_NO_SPLIT and cIdx is equal to 0), the following applies:            -   nW=nCbW            -   nH=nCbH    -   The variable whRatio is set equal to Abs(Log 2(nW/nH)).    -   The variable wideAngle is set equal to 0.    -   For non-square blocks (nW is not equal to nH), the intra        prediction mode predModeIntra is modified as follows:        -   If all of the following conditions are true, wideAngle is            set equal to 1 and predModeIntra is set equal to            (predModeIntra+65).            -   nW is greater than nH            -   predModeIntra is greater than or equal to 2            -   predModeIntra is less than (whRatio>1)?(8+2*whRatio):8        -   Otherwise, if all of the following conditions are true,            wideAngle is set equal to 1 and predModeIntra is set equal            to (predModeIntra−67).            -   nH is greater than nW            -   predModeIntra is less than or equal to 66            -   predModeIntra is greater than                (whRatio>1)?(60−2*whRatio):60

The process of modifying intra prediction mode (predModeIntra) withrespect to the aspect ratio (whRatio) described above would be furtherreferred to as “wide-angle mapping”.

If to apply the state of the art approach, intra prediction directionfor chroma samples may be opposite to the direction specified forcollocated luma samples, because conditions for luma and chroma blockswould be different due to horizontal chroma subsampling as specified forYUV 4:2:2 chroma format.

The embodiments of the disclosure proposes to jointly consider blockaspect ratio and chroma subsampling format when using luma intraprediction mode for chroma intra prediction.

The disclosure provides several methods/embodiments to solve thisproblem. One method introduces clipping operation in order to guaranteethat luma and chroma directional intra prediction uses the same side ofthe block.

Another method includes modification of the wide-angle mapping processin order to guarantee that resulting chroma prediction mode has the sameangle of the mapped direction. As follows from the description above,these directions do not coincide. (“(predModeIntra−67)” and“(predModeIntra+65)”).

The third method includes adjustment of input parameters for wide-anglemapping process. Specifically, it is proposed to use luma aspect ratioinstead of chroma one. In addition, the intraPredAngle parameter is leftor right shifted to compensate for the effect of chroma subsampling.

Alternatively, for the set of signaled luma intra prediction modes givenin VVC specification draft (which are in the range of 0 . . . 66), thefollowing lookup table could be used (Table 5)

TABLE 5 Specification of the LUT for intra prediction mode mapping for4:2:2 chroma format in case of 66 signaled intra prediction directionsIntraPredModeY 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17IntraPredModeC 0 1 2 2 2 2 2 2 2 3 4 6 8 10 12 13 14 16 IntraPredModeY18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 IntraPredModeC 1820 22 23 24 26 28 30 32 33 34 35 36 37 38 39 40 41 IntraPredModeY 36 3738 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 IntraPredModeC 42 43 4444 44 45 46 46 46 47 48 48 48 49 50 51 52 52 IntraPredModeY 54 55 56 5758 59 60 61 62 63 64 65 66 IntraPredModeC 52 53 54 54 54 55 56 56 56 5758 59 60

One of the possible solution includes applying LUT specified in table 5to the value of luma intra prediction mode (IntraPredModeY) and to usethe obtained mode as an input intra prediction mode (IntraPredModeC) ofdirectional intra prediction process for chroma block, that comprises:

-   -   wide-angle mapping of IntraPredModeC    -   derivation of reference sample array (“ref”) and intraPredAngle        parameter    -   obtaining the values of predicted chroma samples using        above-determined reference samples (“ref”) and intraPredAngle        parameter.

This approach works well if when luma intra prediction mode(IntraPredModeY) is not a wide-angle mode. As shown in FIG. 9 ,predicted chroma and luma samples on the same spatial positions “A”would use reference samples that are also located on the same spatialpositions.

This method also works in the case shown in FIG. 11 , because itspecifies clipping of output chroma intra prediction direction to theangle of 45 degrees (mode 2). This clipping is implemented by the meansof specifying the same value for a set of entries in the LUT (please,notice entries IntraPredModeY=2 . . . 8).

Another embodiment of the disclosure includes modification of wide-anglemapping process for the case when operation “wide-angle mapping ofIntraPredModeC” is performed.

The following description specifies the additional dependency ofwide-angle mapping process on whether the mapped direction is performedfor chroma intra prediction for chroma format specifying differentsubsampling ratios in horizontal and vertical directions (denotedfurther as “SubWidthC” and “SubHeightC”, respectively):

The variables nW and nH are derived as follows:

-   -   If IntraSubPartitionsSplitType is equal to ISP_NO_SPLIT or cIdx        is not equal to 0, the following applies:        -   nW=nTbW        -   nH=nTbH    -   Otherwise (IntraSubPartitionsSplitType is not equal to        ISP_NO_SPLIT and cIdx is equal to 0), the following applies:        -   nW=nCbW        -   nH=nCbH            If SubWidthC is not equal to SubHeightC, the value of            variable modeDelta is set to (cIdx==0?0:1), otherwise            modeDelta is set to 0.            The variable whRatio is set equal to Abs(Log 2(nW/nH)).            The variable wideAngle is set equal to 0.            For non-square blocks (nW is not equal to nH), the intra            prediction mode predModeIntra is modified as follows:    -   If all of the following conditions are true, wideAngle is set        equal to 1 and predModeIntra is set equal to        (predModeIntra+65+modeDelta).        -   nW is greater than nH        -   predModeIntra is greater than or equal to 2        -   predModeIntra is less than (whRatio>1)?(8+2*whRatio):8    -   Otherwise, if all of the following conditions are true,        wideAngle is set equal to 1 and predModeIntra is set equal to        (predModeIntra−67+modeDelta).        -   nH is greater than nW        -   predModeIntra is less than or equal to 66        -   predModeIntra is greater than (whRatio>1)?(60−2*whRatio):60

However, approaches described above may result in an opposite directionof luma and chroma intra prediction modes in case when luma intraprediction mode (IntraPredModeY) corresponds to wide-angle direction.FIG. 8 shows an example of the case when IntraPredModeC is derived fromIntraPredModeY where IntraPredModeY is wide-angle intra prediction modeand IntraPredModeC is a non-wide-angle angle intra prediction mode. Theexample of the case when expected intra prediction mode (as shown inFIG. 8 ) is not produced by the method disclosed above. FIG. 9 shows anexample of the case when IntraPredModeC is derived from IntraPredModeYwhere IntraPredModeY is non-wide-angle intra prediction mode andIntraPredModeC is a non-wide-angle angle intra prediction mode. FIG. 10shows an example of the case when IntraPredModeC is derived fromIntraPredModeY where IntraPredModeY is non-wide-angle intra predictionmode and IntraPredModeC is a wide-angle angle intra prediction mode. Theexample of the case (as shown in FIG. 10 ) when non-wide angle inputluma intra prediction mode (IntraPredModeY) produces wide-angle chromaintra prediction mode (IntraPredModeC). FIG. 11 shows an example of thecase when IntraPredModeC is derived from IntraPredModeY using predictionmode clipping and where IntraPredModeY is non-wide-angle intraprediction mode and IntraPredModeC is a non-wide-angle angle intraprediction mode.

-   -   An embodiment specifying the method (“Method 3”) shown in FIG. 8        and FIG. 10 could be disclosed in a form of the following        operations when chroma format is defined as YUV 4:2:2 and input        luma intra prediction mode (IntraPredModeY) is directional (i.e        not equal to DC and not equal to PLANAR): wide-angle mapping of        (IntraPredModeY) using aspect ratio of a luma block resulting        IntraPredModeFinalY;    -   derivation of reference sample array (“ref”) and intraPredAngle        parameter for chroma block using input prediction mode        IntraPredModeFinalY, comprising the following operations:        -   in case when IntraPredModeFinalY is not less than 34,            intraPredAngle parameter is redefined as follows:        -   intraPredAngle=intraPredAngle>>1        -   otherwise, intraPredAngle parameter is redefined as follows        -   intraPredAngle=intraPredAngle<<1    -   obtaining the values of predicted chroma samples using        above-determined reference samples (“ref”) and intraPredAngle        parameter.

Alternatively, instead of “intraPredAngle=intraPredAngle>>1” operationother division by 2 implementation may be used, such as:“intraPredAngle=sign(intraPredAngle)*((Abs(intraPredAngle)+1)>>1)” or“intraPredAngle=intraPredAngle/2”.

A combination of the both methods cold be also applied. An embodimentwould comprise the following operations for an input luma intraprediction mode (IntraPredModeY) that is directional (i.e not equal toDC and not equal to PLANAR):

-   -   if IntraPredModeY is not less than 18 and not greater than 50,        the following operations apply        -   fetch from the LUT (e.g. as specified in table 5) using the            key value of luma intra prediction mode (IntraPredModeY)            resulting in chroma input intra prediction mode            (IntraPredModeC)        -   wide-angle mapping of IntraPredModeC        -   derivation of reference sample array (“ref”) and            intraPredAngle parameter        -   obtaining the values of predicted chroma samples using            above-determined reference samples (“ref”) and            intraPredAngle parameter.    -   Otherwise, perform operations specified in “Method 3”        description.

An embodiment of the disclosure could be also represented in thefollowing form:

8.4.3 Derivation Process for Chroma Intra Prediction Mode

Input to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current chroma coding block relative to the top-left luma sample        of the current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.        In this process, the chroma intra prediction mode        IntraPredModeC[xCb][yCb] is derived.        The chroma intra prediction mode IntraPredModeC[xCb][yCb] is        derived using intra_chroma_pred_mode[xCb][yCb] and        IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2] as specified in        Table 8-2 and Table 8-3.        The chroma intra prediction mode IntraPredModeC[xCb][yCb] is        derived using process map422.

TABLE 8-2 Specification of IntraPredModeC[ xCb ][ yCb] depending onintra_chroma_pred_mode[ xCb ][ yCb] and IntraPredModeY[ xCb + cbWidth/2][ yCb + cbHeight/2] when sps_cclm_enabled_flag is equal to 0IntraPredModeY[ xCb + intra_chroma_pred_ cbWidth/2 ][ yCb + cbHeight/2 ]mode[ xCb ][ yCb ] 0 50 18 1 X ( 0 <= X <= 66) 0 66 0 0 0 0 1 50 66 5050 50 2 18 18 66 18 18 3 1 1 1 66 1 4 0 50 18 1 X

TABLE 8-3 Specification of IntraPredModeC[ xCb ][ yCb] depending onintra_chroma_pred_mode[ xCb ][ yCb] and IntraPredModeY[ xCb + cbWidth/2][ yCb + cbHeight/2] when sps_cclm_enabled_flag is equal to 1IntraPredModeY[ xCb + intra_chroma_pred_ cbWidth/2 ][ yCb + cbHeight/2 ]mode[ xCb ][ yCb ] 0 50 18 1 X ( 0 <= X <= 66) 0 66 0 0 0 0 1 50 66 5050 50 2 18 18 66 18 18 3 1 1 1 66 1 4 81 81 81 81 81 5 82 82 82 82 82 683 83 83 83 83 7 0 50 18 1 XIn the mapping process map422( ) output intra prediction mode Y isderived from the input intra prediction mode X as follows:

-   -   Output intra prediction mode Y is set equal to input intra        prediction mode X if one of the following is true:        -   SubWidthC is equal to SubHeightC,        -   X is smaller than 2,        -   X is larger than 66    -   Otherwise, intra prediction mode Y is set equal to the value        according to the lookup table defined in Table 8-4.

TABLE 8-4 Specification of the lookup table for the map422( ) mappingprocess X 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Y 0 1 2 2 2 2 2 22 3 4 6 8 10 12 13 14 16 X 18 19 20 21 22 23 24 25 26 27 28 29 30 31 3233 34 35 Y 18 20 22 23 24 26 28 30 32 33 34 35 36 37 38 39 40 41 X 36 3738 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 Y 42 43 44 44 44 45 4646 46 47 48 48 48 49 50 51 52 52 X 54 55 56 57 58 59 60 61 62 63 64 6566 Y 52 53 54 54 54 55 56 56 56 57 58 59 60

Another embodiment of the disclosure could also be represented in thefollowing form:

8.4.3 Derivation Process for Chroma Intra Prediction Mode

Input to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current chroma coding block relative to the top-left luma sample        of the current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.        In this process, the chroma intra prediction mode        IntraPredModeC[xCb][yCb] is derived.        The chroma intra prediction mode IntraPredModeC[xCb][yCb] is        derived using intra_chroma_pred_mode[xCb][yCb] and        IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2] as specified in        Table 8-2 and Table 8-3.        The chroma intra prediction mode IntraPredModeC[xCb][yCb] is        derived using process map422.

TABLE 8-2 Specification of IntraPredModeC[ xCb ][ yCb] depending onintra_chroma_pred_mode[ xCb ][ yCb] and IntraPredModeY[ xCb + cbWidth/2][ yCb + cbHeight/2] when sps_cclm_enabled_flag is equal to 0IntraPredModeY[ xCb + intra_chroma_pred_ cbWidth/2 ][ yCb + cbHeight/2 ]mode[ xCb ][ yCb ] 0 50 18 1 X ( 0 <= X <= 66) 0 66 0 0 0 0 1 50 66 5050 50 2 18 18 66 18 18 3 1 1 1 66 1 4 0 50 18 1 X

TABLE 8-3 Specification of IntraPredModeC[ xCb ][ yCb] depending onintra_chroma_pred_mode[ xCb ][ yCb] and IntraPredModeY[ xCb + cbWidth/2][ yCb + cbHeight/2] when sps_cclm_enabled_flag is equal to 1IntraPredModeY[ xCb + intra_chroma_pred_ cbWidth/2 ][ yCb + cbHeight/2 ]mode[ xCb ][ yCb ] 0 50 18 1 X ( 0 <= X <= 66) 0 66 0 0 0 0 1 50 66 5050 50 2 18 18 66 18 18 3 1 1 1 66 1 4 81 81 81 81 81 5 82 82 82 82 82 683 83 83 83 83 7 0 50 18 1 X

In the mapping process map422( ) output intra prediction mode Y isderived from the input intra prediction mode X as follows:

-   -   Output intra prediction mode Y is set equal to input intra        prediction mode X if one of the following is true:        -   SubWidthC is equal to SubHeightC,        -   X is smaller than 2,        -   X is larger than 66    -   Otherwise, intra prediction mode Y is set equal to the value        according to the lookup table defined in Table 8-4.        Variable nW is set equal cbWidth, variable nH is set equal        cbHeight. The variable whRatio is set equal to Abs(Log        2(nW/nH)).        For non-square blocks (nW is not equal to nH), clipping of the        output intra prediction mode Y is performed as follows:    -   If all of the following conditions are true, Y is set equal to        ((whRatio>1)?(8+2*whRatio):8):        -   nW is greater than nH        -   Y is greater than or equal to 2        -   Y is less than (whRatio>1)?(8+2*whRatio):8    -   Otherwise, if all of the following conditions are true, Y is set        equal to ((whRatio>1)?(60−2*whRatio):60):        -   nH is greater than nW        -   Y is less than or equal to 66        -   Y is greater than (whRatio>1)?(60−2*whRatio):60

TABLE 8-4 Specification of the lookup table for the map422( ) mappingprocess X 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Y 0 1 2 2 2 2 2 22 3 4 6 8 10 12 13 14 16 X 18 19 20 21 22 23 24 25 26 27 28 29 30 31 3233 34 35 Y 18 20 22 23 24 26 28 30 32 33 34 35 36 37 38 39 40 41 X 36 3738 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 Y 42 43 44 44 44 45 4646 46 47 48 48 48 49 50 51 52 52 X 54 55 56 57 58 59 60 61 62 63 64 6566 Y 52 53 54 54 54 55 56 56 56 57 58 59 60

A method of intraPredAngle parameter adjustment could also beimplemented in the following form:

8.4.4.2.7 Specification of INTRA_ANGULAR2 . . . INTRA_ANGULAR66 IntraPrediction Modes

Inputs to this process are:

-   -   the intra prediction mode predModeIntra,    -   a variable refIdx specifying the intra prediction reference line        index,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable refW specifying the reference samples width,    -   a variable refH specifying the reference samples height,    -   a variable nCbW specifying the coding block width,    -   a variable nCbH specifying the coding block height,    -   a variable cIdx specifying the colour component of the current        block,    -   the neighbouring samples p[x][y], with x=−1−refIdx, y=−1−refIdx        . . . refH−1 and x=−refIdx . . . refW−1, y=−1−refIdx.        Outputs of this process are the modified intra prediction mode        predModeIntra and the predicted samples predSamples[x][y], with        x=0 . . . nTbW−1, y=0 . . . nTbH−1.        The variable nTbS is set equal to (Log 2 (nTbW)+Log 2        (nTbH))>>1.        The variables nW and nH are derived as follows:    -   If IntraSubPartitionsSplitType is equal to ISP_NO_SPLIT or cIdx        is not equal to 0, the following applies:        -   nW=nTbW        -   nH=nTbH    -   Otherwise (IntraSubPartitionsSplitType is not equal to        ISP_NO_SPLIT and cIdx is equal to 0), the following applies:        -   nW=nCbW        -   nH=nCbH            The variable whRatio is set equal to Abs(Log 2(nW/nH)).            If cIdx is not equal to 0 and subWidthC is greater than            subHeightC, whRatio is incremented by 1.            The variable wideAngle is set equal to 0.            For non-square blocks (nW is not equal to nH), the intra            prediction mode predModeIntra is modified as follows:    -   If all of the following conditions are true, wideAngle is set        equal to 1 and predModeIntra is set equal to (predModeIntra+65).        -   nW is greater than nH        -   predModeIntra is greater than or equal to 2        -   predModeIntra is less than (whRatio>1)?(8+2*whRatio):8    -   Otherwise, if all of the following conditions are true,        wideAngle is set equal to 1 and predModeIntra is set equal to        (predModeIntra−67).        -   nH is greater than nW        -   predModeIntra is less than or equal to 66        -   predModeIntra is greater than (whRatio>1)?(60−2*whRatio):60            The variable filterFlag is derived as follows:    -   If one or more of the following conditions is true, filterFlag        is set equal to 0.        -   predModeIntra is equal to INTRA_ANGULAR2, INTRA_ANGULAR34 or            INTRA_ANGULAR66        -   refIdx is not equal to 0        -   IntraSubPartitionsSplitType is not equal to ISP_NO_SPLIT and            cIdx is equal to 0 and predModeIntra is greater than or            equal to INTRA_ANGULAR34 and nW is greater than 8        -   IntraSubPartitionsSplitType is not equal to ISP_NO_SPLIT and            cIdx is equal to 0 and predModeIntra is less than            INTRA_ANGULAR34 and nH is greater than 8.    -   Otherwise, the following applies:        -   The variable minDistVerHor is set equal to            Min(Abs(predModeIntra−50), Abs(predModeIntra−18)).        -   The variable intraHorVerDistThres[nTbS] is specified in            Table 6.        -   The variable filterFlag is derived as follows:            -   If minDistVerHor is greater than                intraHorVerDistThres[nTbS] or wideAngle is equal to 1,                filterFlag is set equal to 1.            -   Otherwise, filterFlag is set equal to 0.

TABLE 6 Specification of intraHorVerDistThres[ nTbS ] for varioustransform block sizes nTbS nTbS = 2 nTbS = 3 nTbS = 4 nTbS = 5 nTbS = 6nTbS = 7 intraHorVerDistThres[ nTbS ] 16 14 2 0 0 0

FIG. 6 illustrates the 93 prediction directions, where the dasheddirections are associated with the wide-angle modes that are onlyapplied to non-square blocks.

Table 8-5 specifies the mapping table between predModeIntra and theangle parameter intraPredAngle.

TABLE 8-5 Specification of intraPredAngle predModeIntra −14 −13 −12 −11−10 −9 −8 −7 −6 −5 −4 −3 −2 −1 2 3 4 intraPredAngle 512 341 256 171 128102 86 73 64 57 51 45 39 35 32 29 26 predModeIntra 5 6 7 8 9 10 11 12 1314 15 16 17 18 19 20 21 intraPredAngle 23 20 18 16 14 12 10 8 6 4 3 2 10 −1 −2 −3 predModeIntra 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 3738 intraPredAngle −4 −6 −8 −10 −12 −14 −16 −18 −20 −23 −26 −29 −32 −29−26 −23 −20 predModeIntra 39 40 41 42 43 44 45 46 47 48 49 50 51 52 5354 55 intraPredAngle 18 16 14 12 10 −8 −6 −4 −3 −2 −1 0 1 2 3 4 6predModeIntra 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72intraPredAngle 8 10 12 14 16 18 20 23 26 29 32 35 39 45 51 57 64predModeIntra 73 74 75 76 77 78 79 80 intraPredAngle 73 86 102 128 171256 341 512If cIdx is not equal to 0, and subWidthC is greater than subHeightC thefollowing apply:

-   -   If predModeIntra is greater than or equal to 34, intraPredAngle        is set equal to intraPredAngle>>1    -   Otherwise, intraPredAngle is set equal to intraPredAngle<<1        The inverse angle parameter invAngle is derived based on        intraPredAngle as follows:

${invAngle} = {{Round}\left( \frac{256*32}{intraPredAngle} \right)}$The interpolation filter coefficients fC[phase][j] and fG[phase][j] withphase=0 . . . 31 and j=0 . . . 3 are specified in Table 8-6.

TABLE 8-6 Specification of interpolation filter coefficients fC and fGFractional sample fC interpolation filter coefficients fG interpolationfilter coefficients position p f_(c)[ p ] [ 0 ] f_(c)[ p ] [ 1 ] f_(c)[p ][ 2 ] f_(c)[ p ][ 3 ] fG[ p ] [ 0 ] fG[ p ] [ 1 ] fG[ p ][ 2 ] fG[ p][ 3 ]  0 0 64 0 0 16 32 16 0  1 −1 63 2 0 15 29 17 3  2 −2 62 4 0 15 2917 3  3 −2 60 7 −1 14 29 18 3  4 −2 58 10 −2 13 29 18 4  5 −3 57 12 −213 28 19 4  6 −4 56 14 −2 13 28 19 4  7 −4 55 15 −2 12 28 20 4  8 −4 5416 −2 11 28 20 5  9 −5 53 18 −2 11 27 21 5 10 −6 52 20 −2 10 27 22 5 11−6 49 24 −3 9 27 22 6 12 −6 46 28 −4 9 26 23 6 13 −5 44 29 −4 9 26 23 614 −4 42 30 −4 8 25 24 7 15 −4 39 33 −4 8 25 24 7 16 −4 36 36 −4 8 24 248 17 −4 33 39 −4 7 24 25 8 18 −4 30 42 −4 7 24 25 8 19 −4 29 44 −5 6 2326 9 20 −4 28 46 −6 6 23 26 9 21 −3 24 49 −6 6 22 27 9 22 −2 20 52 −6 522 27 10 23 −2 18 53 −5 5 21 27 11 24 −2 16 54 −4 5 20 28 11 25 −2 15 55−4 4 20 28 12 26 −2 14 56 −4 4 19 28 13 27 −2 12 57 −3 4 19 28 13 28 −210 58 −2 4 18 29 13 29 −1 7 60 −2 3 18 29 14 30 0 4 62 −2 3 17 29 15 310 2 63 −1 3 17 29 15The values of the prediction samples predSamples[x][y], with x=0 . . .nTbW−1, y=0 . . . nTbH−1 are derived as follows:

-   -   If predModeIntra is greater than or equal to 34, the following        ordered operations apply:    -   3. The reference sample array ref[x] is specified as follows:        -   The following applies:            ref[x]=p[−1−refIdx+x][−1−refIdx], with x=0 . . . nTbW+refIdx        -   If intraPredAngle is less than 0, the main reference sample            array is extended as follows:            -   When (nTbH*intraPredAngle)>>5 is less than −1,                ref[x]=p[−1−refIdx][−1−refIdx+((x*invAngle+128)>>8)],                with x=−1 . . . (nTbH*intraPredAngle)>>5                ref[((nTbH*intraPredAngle)>>5)−1]=ref[(nTbH*intraPredAngle)>>5]                ref[nTbW+1+refIdx]=ref[nTbW+refIdx]        -   Otherwise,            ref[x]=p[−1−refIdx+x][−1−refIdx], with x=nTbW+1+refIdx . . .            refW+refIdx            ref[−1]=ref[0]            -   The additional samples ref[refW+refIdx+x] with x=1 . . .                (Max(1, nTbW/nTbH)*refIdx+1) are derived as follows:                ref[refW+refIdx+x]=p[−1+refW][−1−refIdx]    -   4. The values of the prediction samples predSamples[x][y], with        x=0 . . . nTbW−1, y=0 . . . nTbH−1 are derived as follows:        -   The index variable iIdx and the multiplication factor iFact            are derived as follows:            iIdx=((y+1+refIdx)*intraPredAngle)>>5+refIdx            iFact=((y+1+refIdx)*intraPredAngle)&31        -   If cIdx is equal to 0, the following applies:            -   The interpolation filter coefficients fT[j] with j=0 . .                . 3 are derived as follows:                fT[j]=filterFlag?fG[iFact][j]:fC[iFact][j]            -   The value of the prediction samples predSamples[x][y] is                derived as follows:                predSamples[x][y]=Clip1Y(((Σ_(i=0) ³                fT[i]*ref[x+iIdx+i])+32)>>6)        -   Otherwise (cIdx is not equal to 0), depending on the value            of iFact, the following applies:            -   If iFact is not equal to 0, the value of the prediction                samples predSamples[x][y] is derived as follows:                predSamples[x][y]=((32−iFact)*ref[x+iIdx+1+]iFact*ref[x+iIdx+2]+16)>>5            -   Otherwise, the value of the prediction samples                predSamples[x][y] is derived as follows:                predSamples[x][y]=ref[x+iIdx+1]    -   Otherwise (predModeIntra is less than 34), the following ordered        operations apply:    -   3. The reference sample array ref[x] is specified as follows:        -   The following applies:            ref[x]=p[−1−refIdx][−1−refIdx+x], with x=0 . . . nTbH+refIdx        -   If intraPredAngle is less than 0, the main reference sample            array is extended as follows:            -   When (nTbW*intraPredAngle)>>5 is less than −1,                ref[x]=p[−1−refIdx+((x*invAngle+128)>>8)][−1−refIdx],                with x=−1 . . . (nTbW*intraPredAngle)>>5                ref[((nTbW*intraPredAngle)>>5)−1]=ref[(nTbW*intraPredAngle)>>5]  (8-145)                ref[nTbG+1+refIdx]=ref[nTbH+refIdx]        -   Otherwise,            ref[x]=p[−1−refIdx][−1−refIdx+x], with x=nTbH+1+refIdx . . .            refH+refIdx            ref[−1]=ref[0]        -   The additional samples ref[refH+refIdx+x] with x=1 . . .            (Max(1, nTbW/nTbH)*refIdx+1) are derived as follows:            ref[refH+refIdx+x]=p[−1+refH][−1−refIdx]    -   4. The values of the prediction samples predSamples[x][y], with        x=0 . . . nTbW−1, y=0 . . . nTbH−1 are derived as follows:        -   The index variable iIdx and the multiplication factor iFact            are derived as follows:            iIdx=((x+1+refIdx)*intraPredAngle)>>5            iFact=((x+1+refIdx)*intraPredAngle)&31        -   If cIdx is equal to 0, the following applies:            -   The interpolation filter coefficients fT[j] with j=0 . .                . 3 are derived as follows:                fT[j]=filterFlag?fG[iFact][j]:fC[iFact][j]            -   The value of the prediction samples predSamples[x][y] is                derived as follows:                predSamples[x][y]=Clip1Y(((Σ_(i=0) ³                fT[i]*ref[y+iIdx+i])+32)>>6)        -   Otherwise (cIdx is not equal to 0), depending on the value            of iFact, the following applies:            -   If iFact is not equal to 0, the value of the prediction                samples predSamples[x][y] is derived as follows:                predSamples[x][y]=((32−iFact)*ref[y+iIdx+1]+iFact*ref[y+iIdx+2]+16)>>5            -   Otherwise, the value of the prediction samples                predSamples[x][y] is derived as follows:                predSamples[x][y]=ref[y+iIdx+1]

In particular, the following methods and embodiments of predictioncoding of a current block implemented by a decoding or encoding device.The decoding device may be video decoder 30 of FIG. 1A, or decoder 30 ofFIG. 3 . The encoding device may be video encoder 20 of FIG. 1A, orencoder 20 of FIG. 2 .

According to system 1200 (see FIG. 12A), when the value ofidc_chrom_format indicates 4:2:2 chroma format, a chroma intraprediction mode (intraPredModeC) 1203 is derived from a look up table(LUT) 1202 by using an initial intra prediction mode of the chromacomponent. The value of initial intra prediction mode of the chromacomponent may equal to the value of Luma intra prediction modeIntraPredModeY 1201. Table 2, table 3, table 8-2, or table 8-3 gives anexample between the value of initial intra prediction mode of the chromacomponent intra_chroma_pred_mode[xCb][yCb] and the value of Luma intraprediction mode IntraPredModeYIntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

The example for the look up table 1202 is table 5, or table 8-4. Thelook up table includes 67 entries, with index 0-66.

After performing wide-angle mapping 1204 on the Chroma intra predictionmode 1203, a modified Chroma intra prediction mode is obtained. Aparameter intraPredAngle 1205 is obtained based on the modified Chromaintra prediction mode. For example, by using the modified Chroma intraprediction mode as the predModeIntra, intraPredAngle 1205 is obtainedfrom the table 1. Predicted samples of the chroma component are obtainedby performing Chroma directional intra prediction 1206 based on theintraPredAngle parameter.

According to an embodiment 1210 (see FIG. 12B), wide-angular mapping1212 is performed on luma intra prediction mode IntraPredModeY 1211 toobtain a modified IntraPredModeY. When the value of idc_chrom_formatindicates 4:2:2 chroma format, a chroma intra prediction mode(intraPredModeC) 1214 is derived from a look up table (LUT) 1213 byusing the modified IntraPredModeY. The look up table 1213 may have 95entries, with index 0-94.

A parameter intraPredAngle 1215 is obtained based on the Chroma intraprediction mode 1214. For example, by using the Chroma intra predictionmode as the predModeIntra, intraPredAngle 1215 is obtained from thetable 1. Predicted samples of the chroma component are obtained byperforming Chroma directional intra prediction 1216 based on theintraPredAngle parameter.

Referring to FIG. 13 , process 1300 includes the following operations:block 1301, the device obtains the value of a luma intra prediction mode(IntraPredModeY). For example, the device obtains the value ofIntraPredModeY by parsing a bitstream. Block 1302, the device obtainsthe initial intra prediction mode of the chroma component(IntraPredModeC) based on the value of the luma intra prediction mode(IntraPredModeY), for example, based on Table 2, table 3, table 8-2, ortable 8-3. Block 1303, the device derives a chroma intra prediction mode(intraPredModeC) from a look up table (LUT) by using the initial intraprediction mode of the chroma component (intraPredModeC) when the chromaformat is 4:2:2. At the example of table 8-4, the initial intraprediction mode of the chroma component is mode X, a chroma intraprediction mode (intraPredModeC) is mode Y. That means the originalintraPredModeC is adjusted to obtain the intraPredModeC.

Block 1304 includes performing wide-angle mapping on the chroma intraprediction mode (intraPredModeC) to obtain a modified intraPredModeC. Asdisclosed above, the wide-angle mapping includes for non-square blocks(nW is not equal to nH):

If all of the following conditions are true, wideAngle is set equal to 1and predModeIntra is set equal to (predModeIntra+65):

-   -   nW is greater than nH    -   predModeIntra is greater than or equal to 2    -   predModeIntra is less than (whRatio>1)?(8+2*whRatio):8

Otherwise, if all of the following conditions are true, wideAngle is setequal to 1 and predModeIntra is set equal to (predModeIntra−67):

-   -   nH is greater than nW    -   predModeIntra is less than or equal to 66    -   predModeIntra is greater than (whRatio>1)?(60−2*whRatio):60

Block 1305 includes obtaining an intraPredAngle parameter for the chromacomponent based on the modified intraPredModeC. For example, by usingthe modified intraPredModeC as the predModeIntra, intraPredAngle 1215 isobtained from the table 1. Block 1306 includes obtaining predictedsamples of the chroma component based on the intraPredAngle parameter.

Detailed information of this embodiment 1300 is shown in theabove-mentioned embodiments.

FIG. 14 is a block diagram illustrating a device of intra prediction ofa chroma component according to an embodiment. Device 1400 may be videodecoder 30 of FIG. 1A, or decoder 30 of FIG. 3 , or may be video encoder20 of FIG. 1A, or encoder 20 of FIG. 2 . The device 1400 can be used toimplement the embodiment 1200, 1210, 1300 and the other embodimentsdescribed above.

The device of directional intra prediction for chroma component of apicture, includes an obtaining unit 1401, a deriving unit 1402, and amapping unit 1403.

The obtaining unit 1401, configured to obtain an initial intraprediction mode of the chroma component. The deriving unit 1402,configured to derive a chroma intra prediction mode (intraPredModeC)from a look up table (LUT) by using the initial intra prediction mode ofthe chroma component, the chroma component having different subsamplingratios in horizontal and vertical directions. The deriving unit 1402 canbe used to derive the chroma intra prediction modeIntraPredModeC[xCb][yCb] by using intra_chroma_pred_mode[xCb][yCb] andIntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2] as specified in Table 8-2and Table 8-3.

The mapping unit 1403, configured to perform wide-angle mapping on thechroma intra prediction mode (intraPredModeC) to obtain a modifiedintraPredModeC. As an example, the mapping unit 1403 performs thewide-angle mapping on an original intra prediction mode (predModeIntra)to obtain a modified predModeIntra, where the value of the originalpredModeIntra is equal to the value of the chroma intra prediction mode(intraPredModeC).

The obtaining unit 1401, further configured to obtain an intraPredAngleparameter for the chroma component, for example, from a mapping table,based on the modified intraPredModeC; and obtain predicted samples ofthe chroma component based on the intraPredAngle parameter.

The obtaining unit 1401 may also be configured to obtain the value of aluma intra prediction mode (IntraPredModeY) from a bitstream, and thenobtain the initial intra prediction mode of the chroma component basedon the value of the luma intra prediction mode (IntraPredModeY).

The present disclosure provides the following set of aspects:

Embodiment 1. A method of directional intra prediction for chromacomponent of a picture having different subsampling ratios in horizontaland vertical directions, comprising:

-   -   obtaining the array of reference samples (“ref”) and        intraPredAngle parameter for chroma component, wherein        intraPredAngle parameter derivation is adjusted according to the        difference of chroma component subsampling ratios in horizontal        and vertical directions    -   obtain predicted samples of chroma component using the array of        reference samples (“ref”) and intraPredAngle parameter for        chroma component.

Embodiment 2. The method of embodiment 1, wherein the method furthercomprising:

-   -   obtaining the value of luma intra prediction mode        (IntraPredModeY) from the bitstream.

Embodiment 3. The method of embodiment 2, wherein intraPredAngleparameter for chroma component is obtained from chroma intra predictionmode (intraPredModeC) which is derived from the value of luma intraprediction mode (IntraPredModeY).

Embodiment 4. Method of embodiment 3, wherein derivation of chroma intraprediction mode (intraPredModeC) is performed by the means of a fetchfrom a LUT.

Embodiment 5. The method of embodiment 3 or 4, wherein a clippingoperation is performed if the obtained chroma intra prediction mode(intraPredModeC) is wide-angular.

Embodiment 6. The method of embodiment 5, wherein the chroma intraprediction mode is set to the closest non-wide angle mode in case ofintraPredModeC satisfies mapping conditions of the wide-angle mappingprocess.

Embodiment 7. The method of any one of embodiments 1-6, whereinwide-angle mapping is performed for luma intra prediction mode(IntraPredModeY) and resulting intra prediction mode is used to get thevalue of intraPredAngle parameter.

Embodiment 8. The method of embodiment 7, wherein the value ofintraPredAngle parameter is adjusted in accordance with chroma formatand is used to obtain predicted samples of chroma component.

Embodiment 9. The method of embodiment 7 or 8, wherein the chroma formatis defined as YUV 4:2:2.

Embodiment 10. The method of any one of embodiment 7-9, whereinwide-angle mapping of (IntraPredModeY) using aspect ratio of a lumablock resulting in IntraPredModeFinalY.

Embodiment 11. The method of embodiment 10, wherein whenIntraPredModeFinalY is not less than 34, intraPredAngle parameter isdefined as follows:intraPredAngle=intraPredAngle>>1otherwise, intraPredAngle parameter is redefined as followsintraPredAngle=intraPredAngle<<1.

Embodiment 12. The method of any one of embodiments 1-11, wherein theintraPredAngle parameter is left or right shifted to compensate for theeffect of chroma subsampling.

Embodiment 13. The method of any of embodiments 1-12, wherein the chromaintra prediction mode IntraPredModeC[xCb][yCb] is derived usingintra_chromapred_mode[xCb][yCb] andIntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2] as specified in Table 8-2and Table 8-3.

Embodiment 14. The method of any of embodiments 1-12, wherein the chromaintra prediction mode IntraPredModeC[xCb][yCb] is derived using processmap422.

Embodiment 15. The method of any one of embodiments 1-14, wherein fornon-square blocks (nW is not equal to nH), the intra prediction modepredModeIntra is obtained as follows:

-   -   If all of the following conditions are true, wideAngle is set        equal to 1 and predModeIntra is set equal to (predModeIntra+65).        -   nW is greater than nH        -   predModeIntra is greater than or equal to 2        -   predModeIntra is less than (whRatio>1)?(8+2*whRatio):8    -   Otherwise, if all of the following conditions are true,        wideAngle is set equal to 1 and predModeIntra is set equal to        (predModeIntra−67).        -   nH is greater than nW        -   predModeIntra is less than or equal to 66        -   predModeIntra is greater than (whRatio>1)?(60−2*whRatio):60

Chroma mode derivation process in accordance with the method proposed isendowed with beneficial effects as compared with the conventionalapproaches. One of these effects is that the embodiments of thedisclosure provide the minimum number of entries in the LUT that is usedto determine chroma intra prediction mode from the initial luma intraprediction mode. This is achieved by the order of operations performed,i.e., by chrominance intra prediction mode mapping to luminance modebeing performed prior to wide-angular mapping. When applyingchroma-to-luma LUT without wide-angular mapping, it is required tospecify mapping just for square block shape thus limiting required LUTentries to 67.

Besides, in the suggested embodiments, chrominance mode derivation doesnot require to obtain the shape of the collocated luminance block. Inthe conventional method, mapping of luminance intra predictiondirections which is the result of wide-angular mapping process wouldrequire to consider the aspect ratio of luminance block as well. Thereason of this dependency is that wide-angular mapping process requiresinformation about the aspect ratio of the block to determine the valueof mapped intra prediction mode. In embodiments of this disclosure, wideangular mapping is not performed for the input luminance intraprediction mode, and hence, the input luminance intra prediction modecould be obtained by bitstream parsing. Since it is not required tohandle partitioning structure of luminance component, decoding latencyis improved if the suggested order of operations is used.

Following is an explanation of the applications of the encoding methodas well as the decoding method as shown in the above-mentionedembodiments, and a system using them.

FIG. 15 is a block diagram showing a content supply system for realizingcontent distribution service. Content supply system 3100 includescapture device 3102, terminal device 3106, and optionally includesdisplay 3126. The capture device 3102 communicates with the terminaldevice 3106 over communication link 3104. The communication link mayinclude the communication channel 13 described above. The communicationlink 3104 includes but not limited to WIFI, Ethernet, Cable, wireless(3G/4G/5G), USB, or any kind of combination thereof, or the like.

The capture device 3102 generates data, and may encode the data by theencoding method as shown in the above embodiments. Alternatively, thecapture device 3102 may distribute the data to a streaming server (notshown in the Figures), and the server encodes the data and transmits theencoded data to the terminal device 3106. The capture device 3102includes but not limited to camera, smart phone or Pad, computer orlaptop, video conference system, PDA, vehicle mounted device, or acombination of any of them, or the like. For example, the capture device3102 may include the source device 12 as described above. When the dataincludes video, the video encoder 20 included in the capture device 3102may actually perform video encoding processing. When the data includesaudio (i.e., voice), an audio encoder included in the capture device3102 may actually perform audio encoding processing. For some practicalscenarios, the capture device 3102 distributes the encoded video andaudio data by multiplexing them together. For other practical scenarios,for example in the video conference system, the encoded audio data andthe encoded video data are not multiplexed. Capture device 3102distributes the encoded audio data and the encoded video data to theterminal device 3106 separately.

In the content supply system 3100, the terminal device 310 receives andreproduces the encoded data. The terminal device 3106 could be a devicewith data receiving and recovering capability, such as smart phone orPad 3108, computer or laptop 3110, network video recorder (NVR)/digitalvideo recorder (DVR) 3112, TV 3114, set top box (STB) 3116, videoconference system 3118, video surveillance system 3120, personal digitalassistant (PDA) 3122, vehicle mounted device 3124, or a combination ofany of them, or the like capable of decoding the above-mentioned encodeddata. For example, the terminal device 3106 may include the destinationdevice 14 as described above. When the encoded data includes video, thevideo decoder 30 included in the terminal device is prioritized toperform video decoding. When the encoded data includes audio, an audiodecoder included in the terminal device is prioritized to perform audiodecoding processing.

For a terminal device with its display, for example, smart phone or Pad3108, computer or laptop 3110, network video recorder (NVR)/digitalvideo recorder (DVR) 3112, TV 3114, personal digital assistant (PDA)3122, or vehicle mounted device 3124, the terminal device can feed thedecoded data to its display. For a terminal device equipped with nodisplay, for example, STB 3116, video conference system 3118, or videosurveillance system 3120, an external display 3126 is contacted thereinto receive and show the decoded data.

When each device in this system performs encoding or decoding, thepicture encoding device or the picture decoding device, as shown in theabove-mentioned embodiments, can be used.

FIG. 16 is a diagram showing a structure of an example terminal device.After terminal device 3106 receives stream from the capture device 3102,the protocol proceeding unit 3202 analyzes the transmission protocol ofthe stream. The protocol includes but not limited to Real Time StreamingProtocol (RTSP), Hyper Text Transfer Protocol (HTTP), HTTP Livestreaming protocol (HLS), MPEG-DASH, Real-time Transport protocol (RTP),Real Time Messaging Protocol (RTMP), or any kind of combination thereof,or the like.

After the protocol proceeding unit 3202 processes the stream, streamfile is generated. The file is outputted to a demultiplexing unit 3204.The demultiplexing unit 3204 can separate the multiplexed data into theencoded audio data and the encoded video data. As described above, forsome practical scenarios, for example in the video conference system,the encoded audio data and the encoded video data are not multiplexed.In this situation, the encoded data is transmitted to video decoder 3206and audio decoder 3208 without through the demultiplexing unit 3204.

Via the demultiplexing processing, video elementary stream (ES), audioES, and optionally subtitle are generated. The video decoder 3206, whichincludes the video decoder 30 as explained in the above mentionedembodiments, decodes the video ES by the decoding method as shown in theabove-mentioned embodiments to generate video frame, and feeds this datato the synchronous unit 3212. The audio decoder 3208, decodes the audioES to generate audio frame, and feeds this data to the synchronous unit3212. Alternatively, the video frame may store in a buffer (not shown inFIG. Y) before feeding it to the synchronous unit 3212. Similarly, theaudio frame may store in a buffer (not shown in FIG. Y) before feedingit to the synchronous unit 3212.

The synchronous unit 3212 synchronizes the video frame and the audioframe, and supplies the video/audio to a video/audio display 3214. Forexample, the synchronous unit 3212 synchronizes the presentation of thevideo and audio information. Information may code in the syntax usingtime stamps concerning the presentation of coded audio and visual dataand time stamps concerning the delivery of the data stream itself

If subtitle is included in the stream, the subtitle decoder 3210 decodesthe subtitle, and synchronizes it with the video frame and the audioframe, and supplies the video/audio/subtitle to a video/audio/subtitledisplay 3216.

The present disclosure is not limited to the above-mentioned system, andeither the picture encoding device or the picture decoding device in theabove-mentioned embodiments can be incorporated into other system, forexample, a car system.

Mathematical Operators

The mathematical operators used in this application are similar to thoseused in the C programming language. However, the results of integerdivision and arithmetic shift operations are defined more precisely, andadditional operations are defined, such as exponentiation andreal-valued division. Numbering and counting conventions generally beginfrom 0, e.g., “the first” is equivalent to the 0-th, “the second” isequivalent to the 1-th, etc.

Arithmetic Operators

The following arithmetic operators are defined as follows:

-   -   + Addition    -   − Subtraction (as a two-argument operator) or negation (as a        unary prefix operator)    -   * Multiplication, including matrix multiplication    -   x^(y) Exponentiation. Specifies x to the power of y. In other        contexts, such notation is used for superscripting not intended        for interpretation as exponentiation.    -   / Integer division with truncation of the result toward zero.        For example, 7/4 and −7/−4 are truncated to 1 and −7/4 and 7/−4        are truncated to −1.    -   ÷ Used to denote division in mathematical equations where no        truncation or rounding is intended.

$\frac{x}{y}$

-   -    Used to denote division in mathematical equations where no        truncation or rounding is intended.

$\sum\limits_{i = x}^{y}{f(i)}$

-   -    The summation of f(i) with i taking all integer values from x        up to and including y.    -   x % y Modulus. Remainder of x divided by y, defined only for        integers x and y with x>=0 and y>0.

Logical Operators

The following logical operators are defined as follows:

-   -   x && y Boolean logical “and” of x and y    -   x∥y Boolean logical “or” of x and y    -   ! Boolean logical “not”    -   x?y:z If x is TRUE or not equal to 0, evaluates to the value of        y; otherwise, evaluates to the value of z.

Relational Operators

The following relational operators are defined as follows:

-   -   > Greater than    -   >= Greater than or equal to    -   < Less than    -   <= Less than or equal to    -   == Equal to    -   != Not equal to

When a relational operator is applied to a syntax element or variablethat has been assigned the value “na” (not applicable), the value “na”is treated as a distinct value for the syntax element or variable. Thevalue “na” is considered not to be equal to any other value.

Bit-Wise Operators

The following bit-wise operators are defined as follows:

-   -   & Bit-wise “and”. When operating on integer arguments, operates        on a two's complement representation of the integer value. When        operating on a binary argument that contains fewer bits than        another argument, the shorter argument is extended by adding        more significant bits equal to 0.    -   | Bit-wise “or”. When operating on integer arguments, operates        on a two's complement representation of the integer value. When        operating on a binary argument that contains fewer bits than        another argument, the shorter argument is extended by adding        more significant bits equal to 0.    -   {circumflex over ( )} A Bit-wise “exclusive or”. When operating        on integer arguments, operates on a two's complement        representation of the integer value. When operating on a binary        argument that contains fewer bits than another argument, the        shorter argument is extended by adding more significant bits        equal to 0.    -   x>>y Arithmetic right shift of a two's complement integer        representation of x by y binary digits. This function is defined        only for non-negative integer values of y. Bits shifted into the        most significant bits (MSBs) as a result of the right shift have        a value equal to the MSB of x prior to the shift operation.    -   x<<y Arithmetic left shift of a two's complement integer        representation of x by y binary digits. This function is defined        only for non-negative integer values of y. Bits shifted into the        least significant bits (LSBs) as a result of the left shift have        a value equal to 0.

Assignment Operators

The following arithmetic operators are defined as follows:

-   -   = Assignment operator    -   ++ Increment, i.e., x++ is equivalent to x=x+1; when used in an        array index, evaluates to the value of the variable prior to the        increment operation.    -   −− Decrement, i.e., x−− is equivalent to x=x−1; when used in an        array index, evaluates to the value of the variable prior to the        decrement operation.    -   += Increment by amount specified, i.e., x+=3 is equivalent to        x=x+3, and x+=(−3) is equivalent to x=x+(−3).    -   −= Decrement by amount specified, i.e., x−=3 is equivalent to        x=x−3, and x−=(−3) is equivalent to x=x−(−3).

Range Notation

The following notation is used to specify a range of values:

-   -   x=y . . . z x takes on integer values starting from y to z,        inclusive, with x, y, and z being integer numbers and z being        greater than y.

Mathematical Functions

The following mathematical functions are defined:

${{Abs}(x)} = \left\{ \begin{matrix}x & ; & {x>=0} \\{- x} & ; & {x < 0}\end{matrix} \right.$

-   -   A sin(x) the trigonometric inverse sine function, operating on        an argument x that is in the range of −1.0 to 1.0, inclusive,        with an output value in the range of −π÷2 to π÷2, inclusive, in        units of radians    -   A tan(x) the trigonometric inverse tangent function, operating        on an argument x, with an output value in the range of −π÷2 to        π÷2, inclusive, in units of radians

${{Atan}\; 2\left( {y,x} \right)} = \left\{ \begin{matrix}{{Atan}\left( \frac{y}{x} \right)} & ; & {x > 0} \\{{{Atan}\left( \frac{y}{x} \right)} + \pi} & ; & {{x < 0}\mspace{14mu}\&\&\mspace{14mu}{y>=0}} \\{{{Atan}\left( \frac{y}{x} \right)} - \pi} & ; & {{x < 0}\mspace{14mu}\&\&\mspace{14mu}{y < 0}} \\{+ \frac{\pi}{2}} & ; & {{x==0}\mspace{14mu}\&\&\mspace{14mu}{y>=0}} \\{- \frac{\pi}{2}} & ; & {otherwise}\end{matrix} \right.$

-   -   Ceil(x) the smallest integer greater than or equal to x.

Clip  1_(Y)(x) = Clip  3(0, (1<<BitDepth_(Y)) − 1, x)Clip  1_(C)(x) = Clip  3(0, (1<<Bitdepth_(C)) − 1, x)${{Clip}\mspace{14mu} 3\left( {x,y,z} \right)} = \left\{ \begin{matrix}x & ; & {z < x} \\y & ; & {z > y} \\z & ; & {otherwise}\end{matrix} \right.$

-   -   Cos(x) the trigonometric cosine function operating on an        argument x in units of radians    -   Floor(x) the largest integer less than or equal to x.

${{GetCurrMsb}\left( {a,b,c,d} \right)} = \left\{ \begin{matrix}{c + d} & ; & {{b - a}>={d/2}} \\{c - d} & ; & {{a - b} > {d/2}} \\c & ; & {otherwise}\end{matrix} \right.$

-   -   Ln(x) the natural logarithm of x (the base-e logarithm, where e        is the natural logarithm base constant 2.718 281 828 . . . ).    -   Log 2(x) the base-2 logarithm of x.    -   Log 10(x) the base-10 logarithm of x.

${{Min}\left( {x,y} \right)} = \left\{ {{\begin{matrix}x & ; & {x<=y} \\y & ; & {x > y}\end{matrix}{{Max}\left( {x,y} \right)}} = \left\{ \begin{matrix}x & ; & {x>=y} \\y & ; & {x < y}\end{matrix} \right.} \right.$

-   -   Round(x)=Sign(x)*Floor(Abs(x)+0.5)

${{Sign}(x)} = \left\{ \begin{matrix}1 & ; & {x > 0} \\0 & ; & {x==0} \\{- 1} & ; & {x < 0}\end{matrix} \right.$

-   -   Sin(x) the trigonometric sine function operating on an argument        x in units of radians    -   Sqrt(x)=√{square root over (x)}    -   Swap(x,y)=(y,x)    -   Tan(x) the trigonometric tangent function operating on an        argument x in units of radians

Order of Operation Precedence

When an order of precedence in an expression is not indicated explicitlyby use of parentheses, the following rules apply:

-   -   Operations of a higher precedence are evaluated before any        operation of a lower precedence.    -   Operations of the same precedence are evaluated sequentially        from left to right.

The table below specifies the precedence of operations from highest tolowest; a higher position in the table indicates a higher precedence.

For those operators that are also used in the C programming language,the order of precedence used in this Specification is the same as usedin the C programming language.

TABLE Operation precedence from highest (at top of table) to lowest (atbottom of table) operations (with operands x, y, and z) ″x++″, +″x− −″″!x″, ″−x″(as a unary prefix operator) x^(y) ″x * y″, ″x / y″, ″x ÷ y″,″ x/y″, ″x % y″ ″x + y″, ″x − y″(as a two-argument operator), ″$\sum\limits_{i = x}^{y}\;{f\left( (i) \right.}$ ″ ″x << y″, ″x >> y″ ″x< y″, ″x <= y″, ″x > y″, ″x >= y″ ″x = = y″, ″x ! = y″ ″x & y″ ″x | y″″x && y″ ″x | | y″ ″x ? y : z″ ″x..y″ ″x = y″, ″x += y″, ″x −= y″

Text Description of Logical Operations

In the text, a statement of logical operations as would be describedmathematically in the following form:

-   -   if(condition 0)        -   statement 0    -   else if(condition 1)        -   statement 1    -   . . .        -   else /* informative remark on remaining condition */            -   statement n                may be described in the following manner:    -   . . . as follows/ . . . the following applies:        -   If condition 0, statement 0        -   Otherwise, if condition 1, statement 1        -   . . .        -   Otherwise (informative remark on remaining condition),            statement n

Each “If . . . Otherwise, if . . . Otherwise, . . . ” statement in thetext is introduced with “ . . . as follows” or “ . . . the followingapplies” immediately followed by “If . . . ”. The last condition of the“If . . . Otherwise, if . . . Otherwise, . . . ” is always an“Otherwise, . . . ”. Interleaved “If . . . Otherwise, if . . .Otherwise, . . . ” statements can be identified by matching “ . . . asfollows” or “ . . . the following applies” with the ending “Otherwise, .. . ”.

In the text, a statement of logical operations as would be describedmathematically in the following form:

-   -   if(condition 0a && condition 0b)        -   statement 0    -   else if(condition 1a∥condition 1b)        -   statement 1    -   . . .    -   else        -   statement n            may be described in the following manner:    -   . . . as follows/ . . . the following applies:        -   If all of the following conditions are true, statement 0:            -   condition 0a            -   condition 0b        -   Otherwise, if one or more of the following conditions are            true, statement 1:            -   condition 1a            -   condition 1b        -   . . .        -   Otherwise, statement n

In the text, a statement of logical operations as would be describedmathematically in the following form:

-   -   if(condition 0)        -   statement 0    -   if(condition 1)        -   statement 1            may be described in the following manner:    -   When condition 0, statement 0    -   When condition 1, statement 1

Although embodiments of the disclosure have been primarily describedbased on video coding, it should be noted that embodiments of the codingsystem 10, encoder 20 and decoder 30 (and correspondingly the system 10)and the other embodiments described herein may also be configured forstill picture processing or coding, i.e. the processing or coding of anindividual picture independent of any preceding or consecutive pictureas in video coding. In general only inter-prediction units 244 (encoder)and 344 (decoder) may not be available in case the picture processingcoding is limited to a single picture 17. All other functionalities(also referred to as tools or technologies) of the video encoder 20 andvideo decoder 30 may equally be used for still picture processing, e.g.residual calculation 204/304, transform 206, quantization 208, inversequantization 210/310, (inverse) transform 212/312, partitioning 262/362,intra-prediction 254/354, and/or loop filtering 220, 320, and entropycoding 270 and entropy decoding 304.

Embodiments, e.g. of the encoder 20 and the decoder 30, and functionsdescribed herein, e.g. with reference to the encoder 20 and the decoder30, may be implemented in hardware, software, firmware, or anycombination thereof. If implemented in software, the functions may bestored on a computer-readable medium or transmitted over communicationmedia as one or more instructions or code and executed by ahardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limiting, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

What is claimed is:
 1. A method of directional intra prediction forchroma component of a picture, the method comprising: obtaining aninitial intra prediction mode of the chroma component of the picture;deriving a chroma intra prediction mode (intraPredModeC) from a look uptable (LUT) by using the initial intra prediction mode of the chromacomponent, wherein a horizontal direction of the chroma component(SubWidthC) is different from a vertical direction of the chromacomponent (SubHeightC); performing wide-angle mapping on theintraPredModeC to obtain a modified intraPredModeC; obtaining an angleparameter for the chroma component based on the modified intraPredModeC;and obtaining predicted samples of the chroma component based on theangle parameter.
 2. The method of claim 1, wherein the method furthercomprises: obtaining a value of a luma intra prediction mode(IntraPredModeY) from a bitstream; wherein obtaining the initial intraprediction mode of the chroma component of the picture comprises:obtaining the initial intra prediction mode of the chroma componentbased on the value of the IntraPredModeY.
 3. The method of claim 1,wherein performing the wide-angle mapping on the intraPredModeC toobtain the modified intraPredModeC comprises: performing wide-anglemapping on an original intra prediction mode (predModeIntra) to obtain amodified predModeIntra, wherein a value of the original predModeIntra isequal to a value of the intraPredModeC.
 4. The method of claim 3,wherein obtaining the angle parameter for the chroma componentcomprises: obtaining the angle parameter for the chroma component from amapping table by using the modified predModeIntra.
 5. The method ofclaim 2, wherein wide-angle mapping is performed for the IntraPredModeYand a resulting intra prediction mode is used to get a value of theangle parameter.
 6. The method of claim 1, wherein the chroma intraprediction mode IntraPredModeC[xCb][yCb] is derived by usingintra_chromapred_mode[xCb][yCb] andIntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2] according to Table 8-2 andTable 8-3.
 7. The method of claim 1, wherein the LUT has 67 entries, anindex for the LUT is a value of 0 to
 66. 8. The method of claim 1,wherein the LUT includes: X 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25Y 6 8 10 12 13 14 16 18 20 22 23 24 26 28 30

wherein mode X is the initial intra prediction mode of the chromacomponent, mode Y is the intraPredModeC derived from the LUT.
 9. Themethod of claim 3, wherein performing the wide-angle mapping on theoriginal predModeIntra to obtain the modified predModeIntra comprises:for non-square blocks, setting the modified predModeIntra to (theoriginal predModeIntra+65) when all of the following are true: avariable nW is greater than a variable nH, the original predModeIntra isgreater than or equal to 2, and the original predModeIntra is less than(a variable whRatio>1)?(8+2*the variable whRatio):8; or setting themodified predModeIntra to (the original predModeIntra−67) when all ofthe following are true: the variable nH is greater than the variable nW,the original predModeIntra is less than or equal to 66, and the originalpredModeIntra is greater than (the variable whRatio>1)?(60−2*thevariable whRatio):60; wherein the variable whRatio is set equal toAbs(Log 2(the variable nW/the variable nH)).
 10. The method of claim 1,wherein a chroma format of the chroma component is defined as YUV 4:2:2.11. A device, comprising: one or more processors; and a non-transitorycomputer-readable storage medium coupled to the one or more processorsand storing programming instructions, which when executed by the one ormore processors, cause the device to: obtain an initial intra predictionmode of a chroma component of a picture; derive a chroma intraprediction mode (intraPredModeC) from a look up table (LUT) by using theinitial intra prediction mode of the chroma component, wherein ahorizontal direction of the chroma component (SubWidthC) is differentfrom a vertical direction of the chroma component (SubHeightC); performwide-angle mapping on the intraPredModeC to obtain a modifiedintraPredModeC; obtain an angle parameter for the chroma component basedon the modified intraPredModeC; and obtain predicted samples of thechroma component based on the angle parameter.
 12. The device of claim11, wherein the programming instructions, which when executed by the oneor more processors, further cause the device to: obtain a value of aluma intra prediction mode (IntraPredModeY) from a bitstream; wherein toobtain the initial intra prediction mode of the chroma component, theprogramming instructions, which when executed by the one or moreprocessors, cause the device to obtain the initial intra prediction modeof the chroma component based on the value of the IntraPredModeY. 13.The device of claim 11, wherein to perform the wide-angle mapping on theintraPredModeC to obtain the modified intraPredModeC, the programminginstructions, which when executed by the one or more processors, causethe device to: perform wide-angle mapping on an original intraprediction mode (predModeIntra) to obtain a modified predModeIntra,wherein a value of the original predModeIntra is equal to a value of thechroma intra prediction mode (intraPredModeC).
 14. The device of claim13, wherein to obtain the angle parameter for the chroma component, theprogramming instructions, which when executed by the one or moreprocessors, cause the device to: obtain the angle parameter for thechroma component from a mapping table by using the modifiedpredModeIntra.
 15. The device of claim 13, wherein the angle parameteris left or right shifted to compensate for an effect of chromasubsampling.
 16. The device of claim 11, wherein to derive theintraPredModeC from the LUT, the programming instructions, which whenexecuted by the one or more processors, cause the device to: derive thechroma intra prediction mode IntraPredModeC[xCb][yCb] by usingintra_chromapred_mode[xCb][yCb] andIntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2] according to Table 8-2 andTable 8-3.
 17. The device of claim 11, wherein the LUT includes: X 11 1213 14 15 16 17 18 19 20 21 22 23 24 25 Y 6 8 10 12 13 14 16 18 20 22 2324 26 28 30

wherein mode X is the initial intra prediction mode of the chromacomponent, mode Y is the intraPredModeC derived from the LUT.
 18. Thedevice of claim 13, wherein to perform the wide-angle mapping on theoriginal predModeIntra to obtain the modified predModeIntra, theprogramming instructions, which when executed by the one or moreprocessors, cause the device to: set the modified predModeIntra to (theoriginal predModeIntra+65) when all of the following are true: avariable nW is greater than a variable nH, the original predModeIntra isgreater than or equal to 2, and the original predModeIntra is less than(a variable whRatio>1)?(8+2*the variable whRatio):8; or set the modifiedpredModeIntra to (the original predModeIntra−67) when all of thefollowing are true: the variable nH is greater than the variable nW, theoriginal predModeIntra is less than or equal to 66, and the originalpredModeIntra is greater than (the variable whRatio>1)?(60−2*thevariable whRatio):60; wherein the variable whRatio is set equal toAbs(Log 2(the variable nW/the variable nH)).
 19. The device of claim 11,wherein a chroma format of the chroma component is defined as YUV 4:2:2.20. The device of claim 11, wherein the device is an encoder or adecoder.